diff --git a/changelog/unreleased/issue-3397 b/changelog/unreleased/issue-3397
new file mode 100644
index 000000000..391eeb004
--- /dev/null
+++ b/changelog/unreleased/issue-3397
@@ -0,0 +1,11 @@
+Enhancement: Improve the ETA displayed during backup
+
+Restic's `backup` command displayed an ETA that did not adapt when the rate
+of progress made during the backup changed during the course of the
+backup. Restic now uses recent progress when computing the ETA. It is
+important to realize that the estimate may still be wrong, because restic
+cannot predict the future, but the hope is that the ETA will be more
+accurate in most cases.
+
+https://github.com/restic/restic/issues/3397
+https://github.com/restic/restic/pull/3563
diff --git a/changelog/unreleased/pull-3261 b/changelog/unreleased/pull-3261
new file mode 100644
index 000000000..f7073ed7b
--- /dev/null
+++ b/changelog/unreleased/pull-3261
@@ -0,0 +1,8 @@
+Enhancement: Reduce file fragmentation for local backend
+
+Before this change, local backend files could become fragmented.
+Now restic will try to preallocate space for pack files to avoid
+their fragmentation.
+
+https://github.com/restic/restic/issues/2679
+https://github.com/restic/restic/pull/3261
diff --git a/cmd/restic/global.go b/cmd/restic/global.go
index 792cf23ac..e898ad9ad 100644
--- a/cmd/restic/global.go
+++ b/cmd/restic/global.go
@@ -536,170 +536,21 @@ func OpenRepository(ctx context.Context, opts GlobalOptions) (*repository.Reposi
 }
 
 func parseConfig(loc location.Location, opts options.Options) (interface{}, error) {
-	// only apply options for a particular backend here
-	opts = opts.Extract(loc.Scheme)
-
-	switch loc.Scheme {
-	case "local":
-		cfg := loc.Config.(local.Config)
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
+	cfg := loc.Config
+	if cfg, ok := cfg.(restic.ApplyEnvironmenter); ok {
+		if err := cfg.ApplyEnvironment(""); err != nil {
 			return nil, err
 		}
-
-		debug.Log("opening local repository at %#v", cfg)
-		return cfg, nil
-
-	case "sftp":
-		cfg := loc.Config.(sftp.Config)
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
-			return nil, err
-		}
-
-		debug.Log("opening sftp repository at %#v", cfg)
-		return cfg, nil
-
-	case "s3":
-		cfg := loc.Config.(s3.Config)
-		if cfg.KeyID == "" {
-			cfg.KeyID = os.Getenv("AWS_ACCESS_KEY_ID")
-		}
-
-		if cfg.Secret.String() == "" {
-			cfg.Secret = options.NewSecretString(os.Getenv("AWS_SECRET_ACCESS_KEY"))
-		}
-
-		if cfg.KeyID == "" && cfg.Secret.String() != "" {
-			return nil, errors.Fatalf("unable to open S3 backend: Key ID ($AWS_ACCESS_KEY_ID) is empty")
-		} else if cfg.KeyID != "" && cfg.Secret.String() == "" {
-			return nil, errors.Fatalf("unable to open S3 backend: Secret ($AWS_SECRET_ACCESS_KEY) is empty")
-		}
-
-		if cfg.Region == "" {
-			cfg.Region = os.Getenv("AWS_DEFAULT_REGION")
-		}
-
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
-			return nil, err
-		}
-
-		debug.Log("opening s3 repository at %#v", cfg)
-		return cfg, nil
-
-	case "gs":
-		cfg := loc.Config.(gs.Config)
-		if cfg.ProjectID == "" {
-			cfg.ProjectID = os.Getenv("GOOGLE_PROJECT_ID")
-		}
-
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
-			return nil, err
-		}
-
-		debug.Log("opening gs repository at %#v", cfg)
-		return cfg, nil
-
-	case "azure":
-		cfg := loc.Config.(azure.Config)
-		if cfg.AccountName == "" {
-			cfg.AccountName = os.Getenv("AZURE_ACCOUNT_NAME")
-		}
-
-		if cfg.AccountKey.String() == "" {
-			cfg.AccountKey = options.NewSecretString(os.Getenv("AZURE_ACCOUNT_KEY"))
-		}
-
-		if cfg.AccountSAS.String() == "" {
-			cfg.AccountSAS = options.NewSecretString(os.Getenv("AZURE_ACCOUNT_SAS"))
-		}
-
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
-			return nil, err
-		}
-
-		debug.Log("opening gs repository at %#v", cfg)
-		return cfg, nil
-
-	case "swift":
-		cfg := loc.Config.(swift.Config)
-
-		if err := swift.ApplyEnvironment("", &cfg); err != nil {
-			return nil, err
-		}
-
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
-			return nil, err
-		}
-
-		debug.Log("opening swift repository at %#v", cfg)
-		return cfg, nil
-
-	case "b2":
-		cfg := loc.Config.(b2.Config)
-
-		if cfg.AccountID == "" {
-			cfg.AccountID = os.Getenv("B2_ACCOUNT_ID")
-		}
-
-		if cfg.AccountID == "" {
-			return nil, errors.Fatalf("unable to open B2 backend: Account ID ($B2_ACCOUNT_ID) is empty")
-		}
-
-		if cfg.Key.String() == "" {
-			cfg.Key = options.NewSecretString(os.Getenv("B2_ACCOUNT_KEY"))
-		}
-
-		if cfg.Key.String() == "" {
-			return nil, errors.Fatalf("unable to open B2 backend: Key ($B2_ACCOUNT_KEY) is empty")
-		}
-
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
-			return nil, err
-		}
-
-		debug.Log("opening b2 repository at %#v", cfg)
-		return cfg, nil
-	case "rest":
-		cfg := loc.Config.(rest.Config)
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
-			return nil, err
-		}
-
-		debug.Log("opening rest repository at %#v", cfg)
-		return cfg, nil
-	case "rclone":
-		cfg := loc.Config.(rclone.Config)
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
-			return nil, err
-		}
-
-		debug.Log("opening rest repository at %#v", cfg)
-		return cfg, nil
-	case "smb":
-		cfg := loc.Config.(smb.Config)
-		if cfg.User == "" {
-			cfg.User = os.Getenv("RESTIC_SMB_USER")
-		}
-
-		if cfg.Password.String() == "" {
-			cfg.Password = options.NewSecretString(os.Getenv("RESTIC_SMB_PASSWORD"))
-		}
-
-		if cfg.Domain == "" {
-			cfg.Domain = os.Getenv("RESTIC_SMB_DOMAIN")
-		}
-		if cfg.Domain == "" {
-			cfg.Domain = smb.DefaultDomain
-		}
-		if err := opts.Apply(loc.Scheme, &cfg); err != nil {
-			return nil, err
-		}
-
-		debug.Log("opening smb repository at %#v", cfg)
-		return cfg, nil
-
 	}
 
-	return nil, errors.Fatalf("invalid backend: %q", loc.Scheme)
+	// only apply options for a particular backend here
+	opts = opts.Extract(loc.Scheme)
+	if err := opts.Apply(loc.Scheme, cfg); err != nil {
+		return nil, err
+	}
+
+	debug.Log("opening %v repository at %#v", loc.Scheme, cfg)
+	return cfg, nil
 }
 
 // Open the backend specified by a location config.
@@ -728,25 +579,25 @@ func open(ctx context.Context, s string, gopts GlobalOptions, opts options.Optio
 
 	switch loc.Scheme {
 	case "local":
-		be, err = local.Open(ctx, cfg.(local.Config))
+		be, err = local.Open(ctx, *cfg.(*local.Config))
 	case "sftp":
-		be, err = sftp.Open(ctx, cfg.(sftp.Config))
-	case "smb":
-		be, err = smb.Open(ctx, cfg.(smb.Config))
+		be, err = sftp.Open(ctx, *cfg.(*sftp.Config))
 	case "s3":
-		be, err = s3.Open(ctx, cfg.(s3.Config), rt)
+		be, err = s3.Open(ctx, *cfg.(*s3.Config), rt)
 	case "gs":
-		be, err = gs.Open(cfg.(gs.Config), rt)
+		be, err = gs.Open(*cfg.(*gs.Config), rt)
 	case "azure":
-		be, err = azure.Open(ctx, cfg.(azure.Config), rt)
+		be, err = azure.Open(ctx, *cfg.(*azure.Config), rt)
 	case "swift":
-		be, err = swift.Open(ctx, cfg.(swift.Config), rt)
+		be, err = swift.Open(ctx, *cfg.(*swift.Config), rt)
 	case "b2":
-		be, err = b2.Open(ctx, cfg.(b2.Config), rt)
+		be, err = b2.Open(ctx, *cfg.(*b2.Config), rt)
 	case "rest":
-		be, err = rest.Open(cfg.(rest.Config), rt)
+		be, err = rest.Open(*cfg.(*rest.Config), rt)
 	case "rclone":
-		be, err = rclone.Open(cfg.(rclone.Config), lim)
+		be, err = rclone.Open(*cfg.(*rclone.Config), lim)
+	case "smb":
+		be, err = smb.Open(ctx, *cfg.(*smb.Config))
 
 	default:
 		return nil, errors.Fatalf("invalid backend: %q", loc.Scheme)
@@ -806,25 +657,25 @@ func create(ctx context.Context, s string, opts options.Options) (restic.Backend
 	var be restic.Backend
 	switch loc.Scheme {
 	case "local":
-		be, err = local.Create(ctx, cfg.(local.Config))
+		be, err = local.Create(ctx, *cfg.(*local.Config))
 	case "sftp":
-		be, err = sftp.Create(ctx, cfg.(sftp.Config))
-	case "smb":
-		be, err = smb.Create(ctx, cfg.(smb.Config))
+		be, err = sftp.Create(ctx, *cfg.(*sftp.Config))
 	case "s3":
-		be, err = s3.Create(ctx, cfg.(s3.Config), rt)
+		be, err = s3.Create(ctx, *cfg.(*s3.Config), rt)
 	case "gs":
-		be, err = gs.Create(ctx, cfg.(gs.Config), rt)
+		be, err = gs.Create(ctx, *cfg.(*gs.Config), rt)
 	case "azure":
-		be, err = azure.Create(ctx, cfg.(azure.Config), rt)
+		be, err = azure.Create(ctx, *cfg.(*azure.Config), rt)
 	case "swift":
-		be, err = swift.Open(ctx, cfg.(swift.Config), rt)
+		be, err = swift.Open(ctx, *cfg.(*swift.Config), rt)
 	case "b2":
-		be, err = b2.Create(ctx, cfg.(b2.Config), rt)
+		be, err = b2.Create(ctx, *cfg.(*b2.Config), rt)
 	case "rest":
-		be, err = rest.Create(ctx, cfg.(rest.Config), rt)
+		be, err = rest.Create(ctx, *cfg.(*rest.Config), rt)
 	case "rclone":
-		be, err = rclone.Create(ctx, cfg.(rclone.Config))
+		be, err = rclone.Create(ctx, *cfg.(*rclone.Config))
+	case "smb":
+		be, err = smb.Create(ctx, *cfg.(*smb.Config))
 	default:
 		debug.Log("invalid repository scheme: %v", s)
 		return nil, errors.Fatalf("invalid scheme %q", loc.Scheme)
diff --git a/internal/backend/azure/azure_test.go b/internal/backend/azure/azure_test.go
index ada6ec2ca..0fab5da26 100644
--- a/internal/backend/azure/azure_test.go
+++ b/internal/backend/azure/azure_test.go
@@ -18,34 +18,34 @@ import (
 	rtest "github.com/restic/restic/internal/test"
 )
 
-func newAzureTestSuite(t testing.TB) *test.Suite {
+func newAzureTestSuite(t testing.TB) *test.Suite[azure.Config] {
 	tr, err := backend.Transport(backend.TransportOptions{})
 	if err != nil {
 		t.Fatalf("cannot create transport for tests: %v", err)
 	}
 
-	return &test.Suite{
+	return &test.Suite[azure.Config]{
 		// do not use excessive data
 		MinimalData: true,
 
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
-			azcfg, err := azure.ParseConfig(os.Getenv("RESTIC_TEST_AZURE_REPOSITORY"))
+		NewConfig: func() (*azure.Config, error) {
+			cfg, err := azure.ParseConfig(os.Getenv("RESTIC_TEST_AZURE_REPOSITORY"))
+			if err != nil {
+				return nil, err
+			}
+
+			err = cfg.ApplyEnvironment("RESTIC_TEST_")
 			if err != nil {
 				return nil, err
 			}
 
-			cfg := azcfg.(azure.Config)
-			cfg.AccountName = os.Getenv("RESTIC_TEST_AZURE_ACCOUNT_NAME")
-			cfg.AccountKey = options.NewSecretString(os.Getenv("RESTIC_TEST_AZURE_ACCOUNT_KEY"))
 			cfg.Prefix = fmt.Sprintf("test-%d", time.Now().UnixNano())
 			return cfg, nil
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(azure.Config)
-
+		Create: func(cfg azure.Config) (restic.Backend, error) {
 			ctx := context.TODO()
 			be, err := azure.Create(ctx, cfg, tr)
 			if err != nil {
@@ -65,15 +65,13 @@ func newAzureTestSuite(t testing.TB) *test.Suite {
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(azure.Config)
+		Open: func(cfg azure.Config) (restic.Backend, error) {
 			ctx := context.TODO()
 			return azure.Open(ctx, cfg, tr)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
-			cfg := config.(azure.Config)
+		Cleanup: func(cfg azure.Config) error {
 			ctx := context.TODO()
 			be, err := azure.Open(ctx, cfg, tr)
 			if err != nil {
@@ -141,12 +139,11 @@ func TestUploadLargeFile(t *testing.T) {
 		return
 	}
 
-	azcfg, err := azure.ParseConfig(os.Getenv("RESTIC_TEST_AZURE_REPOSITORY"))
+	cfg, err := azure.ParseConfig(os.Getenv("RESTIC_TEST_AZURE_REPOSITORY"))
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	cfg := azcfg.(azure.Config)
 	cfg.AccountName = os.Getenv("RESTIC_TEST_AZURE_ACCOUNT_NAME")
 	cfg.AccountKey = options.NewSecretString(os.Getenv("RESTIC_TEST_AZURE_ACCOUNT_KEY"))
 	cfg.Prefix = fmt.Sprintf("test-upload-large-%d", time.Now().UnixNano())
@@ -156,7 +153,7 @@ func TestUploadLargeFile(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	be, err := azure.Create(ctx, cfg, tr)
+	be, err := azure.Create(ctx, *cfg, tr)
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/internal/backend/azure/config.go b/internal/backend/azure/config.go
index 55b26d4f1..4d4e839ff 100644
--- a/internal/backend/azure/config.go
+++ b/internal/backend/azure/config.go
@@ -1,11 +1,13 @@
 package azure
 
 import (
+	"os"
 	"path"
 	"strings"
 
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/options"
+	"github.com/restic/restic/internal/restic"
 )
 
 // Config contains all configuration necessary to connect to an azure compatible
@@ -33,7 +35,7 @@ func init() {
 
 // ParseConfig parses the string s and extracts the azure config. The
 // configuration format is azure:containerName:/[prefix].
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	if !strings.HasPrefix(s, "azure:") {
 		return nil, errors.New("azure: invalid format")
 	}
@@ -51,5 +53,23 @@ func ParseConfig(s string) (interface{}, error) {
 	cfg := NewConfig()
 	cfg.Container = container
 	cfg.Prefix = prefix
-	return cfg, nil
+	return &cfg, nil
+}
+
+var _ restic.ApplyEnvironmenter = &Config{}
+
+// ApplyEnvironment saves values from the environment to the config.
+func (cfg *Config) ApplyEnvironment(prefix string) error {
+	if cfg.AccountName == "" {
+		cfg.AccountName = os.Getenv(prefix + "AZURE_ACCOUNT_NAME")
+	}
+
+	if cfg.AccountKey.String() == "" {
+		cfg.AccountKey = options.NewSecretString(os.Getenv(prefix + "AZURE_ACCOUNT_KEY"))
+	}
+
+	if cfg.AccountSAS.String() == "" {
+		cfg.AccountSAS = options.NewSecretString(os.Getenv(prefix + "AZURE_ACCOUNT_SAS"))
+	}
+	return nil
 }
diff --git a/internal/backend/azure/config_test.go b/internal/backend/azure/config_test.go
index a57542e77..49cda6571 100644
--- a/internal/backend/azure/config_test.go
+++ b/internal/backend/azure/config_test.go
@@ -1,22 +1,23 @@
 package azure
 
-import "testing"
+import (
+	"testing"
 
-var configTests = []struct {
-	s   string
-	cfg Config
-}{
-	{"azure:container-name:/", Config{
+	"github.com/restic/restic/internal/backend/test"
+)
+
+var configTests = []test.ConfigTestData[Config]{
+	{S: "azure:container-name:/", Cfg: Config{
 		Container:   "container-name",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"azure:container-name:/prefix/directory", Config{
+	{S: "azure:container-name:/prefix/directory", Cfg: Config{
 		Container:   "container-name",
 		Prefix:      "prefix/directory",
 		Connections: 5,
 	}},
-	{"azure:container-name:/prefix/directory/", Config{
+	{S: "azure:container-name:/prefix/directory/", Cfg: Config{
 		Container:   "container-name",
 		Prefix:      "prefix/directory",
 		Connections: 5,
@@ -24,17 +25,5 @@ var configTests = []struct {
 }
 
 func TestParseConfig(t *testing.T) {
-	for i, test := range configTests {
-		cfg, err := ParseConfig(test.s)
-		if err != nil {
-			t.Errorf("test %d:%s failed: %v", i, test.s, err)
-			continue
-		}
-
-		if cfg != test.cfg {
-			t.Errorf("test %d:\ninput:\n  %s\n wrong config, want:\n  %v\ngot:\n  %v",
-				i, test.s, test.cfg, cfg)
-			continue
-		}
-	}
+	test.ParseConfigTester(t, ParseConfig, configTests)
 }
diff --git a/internal/backend/b2/b2_test.go b/internal/backend/b2/b2_test.go
index 123a61d7c..8e982adda 100644
--- a/internal/backend/b2/b2_test.go
+++ b/internal/backend/b2/b2_test.go
@@ -10,19 +10,18 @@ import (
 	"github.com/restic/restic/internal/backend"
 	"github.com/restic/restic/internal/backend/b2"
 	"github.com/restic/restic/internal/backend/test"
-	"github.com/restic/restic/internal/options"
 	"github.com/restic/restic/internal/restic"
 
 	rtest "github.com/restic/restic/internal/test"
 )
 
-func newB2TestSuite(t testing.TB) *test.Suite {
+func newB2TestSuite(t testing.TB) *test.Suite[b2.Config] {
 	tr, err := backend.Transport(backend.TransportOptions{})
 	if err != nil {
 		t.Fatalf("cannot create transport for tests: %v", err)
 	}
 
-	return &test.Suite{
+	return &test.Suite[b2.Config]{
 		// do not use excessive data
 		MinimalData: true,
 
@@ -30,34 +29,33 @@ func newB2TestSuite(t testing.TB) *test.Suite {
 		WaitForDelayedRemoval: 10 * time.Second,
 
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
-			b2cfg, err := b2.ParseConfig(os.Getenv("RESTIC_TEST_B2_REPOSITORY"))
+		NewConfig: func() (*b2.Config, error) {
+			cfg, err := b2.ParseConfig(os.Getenv("RESTIC_TEST_B2_REPOSITORY"))
+			if err != nil {
+				return nil, err
+			}
+
+			err = cfg.ApplyEnvironment("RESTIC_TEST_")
 			if err != nil {
 				return nil, err
 			}
 
-			cfg := b2cfg.(b2.Config)
-			cfg.AccountID = os.Getenv("RESTIC_TEST_B2_ACCOUNT_ID")
-			cfg.Key = options.NewSecretString(os.Getenv("RESTIC_TEST_B2_ACCOUNT_KEY"))
 			cfg.Prefix = fmt.Sprintf("test-%d", time.Now().UnixNano())
 			return cfg, nil
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(b2.Config)
+		Create: func(cfg b2.Config) (restic.Backend, error) {
 			return b2.Create(context.Background(), cfg, tr)
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(b2.Config)
+		Open: func(cfg b2.Config) (restic.Backend, error) {
 			return b2.Open(context.Background(), cfg, tr)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
-			cfg := config.(b2.Config)
+		Cleanup: func(cfg b2.Config) error {
 			be, err := b2.Open(context.Background(), cfg, tr)
 			if err != nil {
 				return err
diff --git a/internal/backend/b2/config.go b/internal/backend/b2/config.go
index ba5141834..548fbef99 100644
--- a/internal/backend/b2/config.go
+++ b/internal/backend/b2/config.go
@@ -1,12 +1,14 @@
 package b2
 
 import (
+	"os"
 	"path"
 	"regexp"
 	"strings"
 
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/options"
+	"github.com/restic/restic/internal/restic"
 )
 
 // Config contains all configuration necessary to connect to an b2 compatible
@@ -58,7 +60,7 @@ func checkBucketName(name string) error {
 // ParseConfig parses the string s and extracts the b2 config. The supported
 // configuration format is b2:bucketname/prefix. If no prefix is given the
 // prefix "restic" will be used.
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	if !strings.HasPrefix(s, "b2:") {
 		return nil, errors.New("invalid format, want: b2:bucket-name[:path]")
 	}
@@ -77,5 +79,27 @@ func ParseConfig(s string) (interface{}, error) {
 	cfg.Bucket = bucket
 	cfg.Prefix = prefix
 
-	return cfg, nil
+	return &cfg, nil
+}
+
+var _ restic.ApplyEnvironmenter = &Config{}
+
+// ApplyEnvironment saves values from the environment to the config.
+func (cfg *Config) ApplyEnvironment(prefix string) error {
+	if cfg.AccountID == "" {
+		cfg.AccountID = os.Getenv(prefix + "B2_ACCOUNT_ID")
+	}
+
+	if cfg.AccountID == "" {
+		return errors.Fatalf("unable to open B2 backend: Account ID ($B2_ACCOUNT_ID) is empty")
+	}
+
+	if cfg.Key.String() == "" {
+		cfg.Key = options.NewSecretString(os.Getenv(prefix + "B2_ACCOUNT_KEY"))
+	}
+
+	if cfg.Key.String() == "" {
+		return errors.Fatalf("unable to open B2 backend: Key ($B2_ACCOUNT_KEY) is empty")
+	}
+	return nil
 }
diff --git a/internal/backend/b2/config_test.go b/internal/backend/b2/config_test.go
index 4194cb62c..f62972005 100644
--- a/internal/backend/b2/config_test.go
+++ b/internal/backend/b2/config_test.go
@@ -1,37 +1,38 @@
 package b2
 
-import "testing"
+import (
+	"testing"
 
-var configTests = []struct {
-	s   string
-	cfg Config
-}{
-	{"b2:bucketname", Config{
+	"github.com/restic/restic/internal/backend/test"
+)
+
+var configTests = []test.ConfigTestData[Config]{
+	{S: "b2:bucketname", Cfg: Config{
 		Bucket:      "bucketname",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"b2:bucketname:", Config{
+	{S: "b2:bucketname:", Cfg: Config{
 		Bucket:      "bucketname",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"b2:bucketname:/prefix/directory", Config{
+	{S: "b2:bucketname:/prefix/directory", Cfg: Config{
 		Bucket:      "bucketname",
 		Prefix:      "prefix/directory",
 		Connections: 5,
 	}},
-	{"b2:foobar", Config{
+	{S: "b2:foobar", Cfg: Config{
 		Bucket:      "foobar",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"b2:foobar:", Config{
+	{S: "b2:foobar:", Cfg: Config{
 		Bucket:      "foobar",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"b2:foobar:/", Config{
+	{S: "b2:foobar:/", Cfg: Config{
 		Bucket:      "foobar",
 		Prefix:      "",
 		Connections: 5,
@@ -39,19 +40,7 @@ var configTests = []struct {
 }
 
 func TestParseConfig(t *testing.T) {
-	for _, test := range configTests {
-		t.Run("", func(t *testing.T) {
-			cfg, err := ParseConfig(test.s)
-			if err != nil {
-				t.Fatalf("%s failed: %v", test.s, err)
-			}
-
-			if cfg != test.cfg {
-				t.Fatalf("input: %s\n wrong config, want:\n  %#v\ngot:\n  %#v",
-					test.s, test.cfg, cfg)
-			}
-		})
-	}
+	test.ParseConfigTester(t, ParseConfig, configTests)
 }
 
 var invalidConfigTests = []struct {
diff --git a/internal/backend/gs/config.go b/internal/backend/gs/config.go
index 8bb2bddea..b2d52c5f8 100644
--- a/internal/backend/gs/config.go
+++ b/internal/backend/gs/config.go
@@ -1,11 +1,13 @@
 package gs
 
 import (
+	"os"
 	"path"
 	"strings"
 
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/options"
+	"github.com/restic/restic/internal/restic"
 )
 
 // Config contains all configuration necessary to connect to a Google Cloud Storage
@@ -34,7 +36,7 @@ func init() {
 
 // ParseConfig parses the string s and extracts the gcs config. The
 // supported configuration format is gs:bucketName:/[prefix].
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	if !strings.HasPrefix(s, "gs:") {
 		return nil, errors.New("gs: invalid format")
 	}
@@ -54,5 +56,15 @@ func ParseConfig(s string) (interface{}, error) {
 	cfg := NewConfig()
 	cfg.Bucket = bucket
 	cfg.Prefix = prefix
-	return cfg, nil
+	return &cfg, nil
+}
+
+var _ restic.ApplyEnvironmenter = &Config{}
+
+// ApplyEnvironment saves values from the environment to the config.
+func (cfg *Config) ApplyEnvironment(prefix string) error {
+	if cfg.ProjectID == "" {
+		cfg.ProjectID = os.Getenv(prefix + "GOOGLE_PROJECT_ID")
+	}
+	return nil
 }
diff --git a/internal/backend/gs/config_test.go b/internal/backend/gs/config_test.go
index fb2774d25..890de577f 100644
--- a/internal/backend/gs/config_test.go
+++ b/internal/backend/gs/config_test.go
@@ -1,24 +1,25 @@
 package gs
 
-import "testing"
+import (
+	"testing"
 
-var configTests = []struct {
-	s   string
-	cfg Config
-}{
-	{"gs:bucketname:/", Config{
+	"github.com/restic/restic/internal/backend/test"
+)
+
+var configTests = []test.ConfigTestData[Config]{
+	{S: "gs:bucketname:/", Cfg: Config{
 		Bucket:      "bucketname",
 		Prefix:      "",
 		Connections: 5,
 		Region:      "us",
 	}},
-	{"gs:bucketname:/prefix/directory", Config{
+	{S: "gs:bucketname:/prefix/directory", Cfg: Config{
 		Bucket:      "bucketname",
 		Prefix:      "prefix/directory",
 		Connections: 5,
 		Region:      "us",
 	}},
-	{"gs:bucketname:/prefix/directory/", Config{
+	{S: "gs:bucketname:/prefix/directory/", Cfg: Config{
 		Bucket:      "bucketname",
 		Prefix:      "prefix/directory",
 		Connections: 5,
@@ -27,17 +28,5 @@ var configTests = []struct {
 }
 
 func TestParseConfig(t *testing.T) {
-	for i, test := range configTests {
-		cfg, err := ParseConfig(test.s)
-		if err != nil {
-			t.Errorf("test %d:%s failed: %v", i, test.s, err)
-			continue
-		}
-
-		if cfg != test.cfg {
-			t.Errorf("test %d:\ninput:\n  %s\n wrong config, want:\n  %v\ngot:\n  %v",
-				i, test.s, test.cfg, cfg)
-			continue
-		}
-	}
+	test.ParseConfigTester(t, ParseConfig, configTests)
 }
diff --git a/internal/backend/gs/gs_test.go b/internal/backend/gs/gs_test.go
index 19ae8b829..f96b6c62b 100644
--- a/internal/backend/gs/gs_test.go
+++ b/internal/backend/gs/gs_test.go
@@ -15,33 +15,30 @@ import (
 	rtest "github.com/restic/restic/internal/test"
 )
 
-func newGSTestSuite(t testing.TB) *test.Suite {
+func newGSTestSuite(t testing.TB) *test.Suite[gs.Config] {
 	tr, err := backend.Transport(backend.TransportOptions{})
 	if err != nil {
 		t.Fatalf("cannot create transport for tests: %v", err)
 	}
 
-	return &test.Suite{
+	return &test.Suite[gs.Config]{
 		// do not use excessive data
 		MinimalData: true,
 
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
-			gscfg, err := gs.ParseConfig(os.Getenv("RESTIC_TEST_GS_REPOSITORY"))
+		NewConfig: func() (*gs.Config, error) {
+			cfg, err := gs.ParseConfig(os.Getenv("RESTIC_TEST_GS_REPOSITORY"))
 			if err != nil {
 				return nil, err
 			}
 
-			cfg := gscfg.(gs.Config)
 			cfg.ProjectID = os.Getenv("RESTIC_TEST_GS_PROJECT_ID")
 			cfg.Prefix = fmt.Sprintf("test-%d", time.Now().UnixNano())
 			return cfg, nil
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(gs.Config)
-
+		Create: func(cfg gs.Config) (restic.Backend, error) {
 			be, err := gs.Create(context.Background(), cfg, tr)
 			if err != nil {
 				return nil, err
@@ -60,15 +57,12 @@ func newGSTestSuite(t testing.TB) *test.Suite {
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(gs.Config)
+		Open: func(cfg gs.Config) (restic.Backend, error) {
 			return gs.Open(cfg, tr)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
-			cfg := config.(gs.Config)
-
+		Cleanup: func(cfg gs.Config) error {
 			be, err := gs.Open(cfg, tr)
 			if err != nil {
 				return err
diff --git a/internal/backend/local/config.go b/internal/backend/local/config.go
index e59d1f693..dc5e7948c 100644
--- a/internal/backend/local/config.go
+++ b/internal/backend/local/config.go
@@ -27,12 +27,12 @@ func init() {
 }
 
 // ParseConfig parses a local backend config.
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	if !strings.HasPrefix(s, "local:") {
 		return nil, errors.New(`invalid format, prefix "local" not found`)
 	}
 
 	cfg := NewConfig()
 	cfg.Path = s[6:]
-	return cfg, nil
+	return &cfg, nil
 }
diff --git a/internal/backend/local/config_test.go b/internal/backend/local/config_test.go
new file mode 100644
index 000000000..c9b6be61c
--- /dev/null
+++ b/internal/backend/local/config_test.go
@@ -0,0 +1,18 @@
+package local
+
+import (
+	"testing"
+
+	"github.com/restic/restic/internal/backend/test"
+)
+
+var configTests = []test.ConfigTestData[Config]{
+	{S: "local:/some/path", Cfg: Config{
+		Path:        "/some/path",
+		Connections: 2,
+	}},
+}
+
+func TestParseConfig(t *testing.T) {
+	test.ParseConfigTester(t, ParseConfig, configTests)
+}
diff --git a/internal/backend/local/local.go b/internal/backend/local/local.go
index be332e8ad..d6bdef1e4 100644
--- a/internal/backend/local/local.go
+++ b/internal/backend/local/local.go
@@ -148,6 +148,13 @@ func (b *Local) Save(_ context.Context, h restic.Handle, rd restic.RewindReader)
 		}
 	}(f)
 
+	// preallocate disk space
+	if size := rd.Length(); size > 0 {
+		if err := fs.PreallocateFile(f, size); err != nil {
+			debug.Log("Failed to preallocate %v with size %v: %v", finalname, size, err)
+		}
+	}
+
 	// save data, then sync
 	wbytes, err := io.Copy(f, rd)
 	if err != nil {
diff --git a/internal/backend/local/local_test.go b/internal/backend/local/local_test.go
index 495f220a0..ca9e3b71b 100644
--- a/internal/backend/local/local_test.go
+++ b/internal/backend/local/local_test.go
@@ -12,10 +12,10 @@ import (
 	rtest "github.com/restic/restic/internal/test"
 )
 
-func newTestSuite(t testing.TB) *test.Suite {
-	return &test.Suite{
+func newTestSuite(t testing.TB) *test.Suite[local.Config] {
+	return &test.Suite[local.Config]{
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
+		NewConfig: func() (*local.Config, error) {
 			dir, err := os.MkdirTemp(rtest.TestTempDir, "restic-test-local-")
 			if err != nil {
 				t.Fatal(err)
@@ -23,7 +23,7 @@ func newTestSuite(t testing.TB) *test.Suite {
 
 			t.Logf("create new backend at %v", dir)
 
-			cfg := local.Config{
+			cfg := &local.Config{
 				Path:        dir,
 				Connections: 2,
 			}
@@ -31,20 +31,17 @@ func newTestSuite(t testing.TB) *test.Suite {
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(local.Config)
+		Create: func(cfg local.Config) (restic.Backend, error) {
 			return local.Create(context.TODO(), cfg)
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(local.Config)
+		Open: func(cfg local.Config) (restic.Backend, error) {
 			return local.Open(context.TODO(), cfg)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
-			cfg := config.(local.Config)
+		Cleanup: func(cfg local.Config) error {
 			if !rtest.TestCleanupTempDirs {
 				t.Logf("leaving test backend dir at %v", cfg.Path)
 			}
diff --git a/internal/backend/location/location.go b/internal/backend/location/location.go
index c9bbf981f..dcc748744 100644
--- a/internal/backend/location/location.go
+++ b/internal/backend/location/location.go
@@ -30,19 +30,25 @@ type parser struct {
 	stripPassword func(string) string
 }
 
+func configToAny[C any](parser func(string) (*C, error)) func(string) (interface{}, error) {
+	return func(s string) (interface{}, error) {
+		return parser(s)
+	}
+}
+
 // parsers is a list of valid config parsers for the backends. The first parser
 // is the fallback and should always be set to the local backend.
 var parsers = []parser{
-	{"b2", b2.ParseConfig, noPassword},
-	{"local", local.ParseConfig, noPassword},
-	{"sftp", sftp.ParseConfig, noPassword},
-	{"s3", s3.ParseConfig, noPassword},
-	{"gs", gs.ParseConfig, noPassword},
-	{"azure", azure.ParseConfig, noPassword},
-	{"swift", swift.ParseConfig, noPassword},
-	{"rest", rest.ParseConfig, rest.StripPassword},
-	{"rclone", rclone.ParseConfig, noPassword},
-	{"smb", smb.ParseConfig, noPassword},
+	{"b2", configToAny(b2.ParseConfig), noPassword},
+	{"local", configToAny(local.ParseConfig), noPassword},
+	{"sftp", configToAny(sftp.ParseConfig), noPassword},
+	{"s3", configToAny(s3.ParseConfig), noPassword},
+	{"gs", configToAny(gs.ParseConfig), noPassword},
+	{"azure", configToAny(azure.ParseConfig), noPassword},
+	{"swift", configToAny(swift.ParseConfig), noPassword},
+	{"rest", configToAny(rest.ParseConfig), rest.StripPassword},
+	{"rclone", configToAny(rclone.ParseConfig), noPassword},
+	{"smb", configToAny(smb.ParseConfig), noPassword},
 }
 
 // noPassword returns the repository location unchanged (there's no sensitive information there)
diff --git a/internal/backend/location/location_test.go b/internal/backend/location/location_test.go
index 809379850..9f5db70c9 100644
--- a/internal/backend/location/location_test.go
+++ b/internal/backend/location/location_test.go
@@ -29,7 +29,7 @@ var parseTests = []struct {
 	{
 		"local:/srv/repo",
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        "/srv/repo",
 				Connections: 2,
 			},
@@ -38,7 +38,7 @@ var parseTests = []struct {
 	{
 		"local:dir1/dir2",
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        "dir1/dir2",
 				Connections: 2,
 			},
@@ -47,7 +47,7 @@ var parseTests = []struct {
 	{
 		"local:dir1/dir2",
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        "dir1/dir2",
 				Connections: 2,
 			},
@@ -56,7 +56,7 @@ var parseTests = []struct {
 	{
 		"dir1/dir2",
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        "dir1/dir2",
 				Connections: 2,
 			},
@@ -65,7 +65,7 @@ var parseTests = []struct {
 	{
 		"/dir1/dir2",
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        "/dir1/dir2",
 				Connections: 2,
 			},
@@ -74,7 +74,7 @@ var parseTests = []struct {
 	{
 		"local:../dir1/dir2",
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        "../dir1/dir2",
 				Connections: 2,
 			},
@@ -83,7 +83,7 @@ var parseTests = []struct {
 	{
 		"/dir1/dir2",
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        "/dir1/dir2",
 				Connections: 2,
 			},
@@ -92,7 +92,7 @@ var parseTests = []struct {
 	{
 		"/dir1:foobar/dir2",
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        "/dir1:foobar/dir2",
 				Connections: 2,
 			},
@@ -101,7 +101,7 @@ var parseTests = []struct {
 	{
 		`\dir1\foobar\dir2`,
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        `\dir1\foobar\dir2`,
 				Connections: 2,
 			},
@@ -110,7 +110,7 @@ var parseTests = []struct {
 	{
 		`c:\dir1\foobar\dir2`,
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        `c:\dir1\foobar\dir2`,
 				Connections: 2,
 			},
@@ -119,7 +119,7 @@ var parseTests = []struct {
 	{
 		`C:\Users\appveyor\AppData\Local\Temp\1\restic-test-879453535\repo`,
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        `C:\Users\appveyor\AppData\Local\Temp\1\restic-test-879453535\repo`,
 				Connections: 2,
 			},
@@ -128,7 +128,7 @@ var parseTests = []struct {
 	{
 		`c:/dir1/foobar/dir2`,
 		Location{Scheme: "local",
-			Config: local.Config{
+			Config: &local.Config{
 				Path:        `c:/dir1/foobar/dir2`,
 				Connections: 2,
 			},
@@ -137,7 +137,7 @@ var parseTests = []struct {
 	{
 		"sftp:user@host:/srv/repo",
 		Location{Scheme: "sftp",
-			Config: sftp.Config{
+			Config: &sftp.Config{
 				User:        "user",
 				Host:        "host",
 				Path:        "/srv/repo",
@@ -148,7 +148,7 @@ var parseTests = []struct {
 	{
 		"sftp:host:/srv/repo",
 		Location{Scheme: "sftp",
-			Config: sftp.Config{
+			Config: &sftp.Config{
 				User:        "",
 				Host:        "host",
 				Path:        "/srv/repo",
@@ -159,7 +159,7 @@ var parseTests = []struct {
 	{
 		"sftp://user@host/srv/repo",
 		Location{Scheme: "sftp",
-			Config: sftp.Config{
+			Config: &sftp.Config{
 				User:        "user",
 				Host:        "host",
 				Path:        "srv/repo",
@@ -170,7 +170,7 @@ var parseTests = []struct {
 	{
 		"sftp://user@host//srv/repo",
 		Location{Scheme: "sftp",
-			Config: sftp.Config{
+			Config: &sftp.Config{
 				User:        "user",
 				Host:        "host",
 				Path:        "/srv/repo",
@@ -182,7 +182,7 @@ var parseTests = []struct {
 	{
 		"s3://eu-central-1/bucketname",
 		Location{Scheme: "s3",
-			Config: s3.Config{
+			Config: &s3.Config{
 				Endpoint:    "eu-central-1",
 				Bucket:      "bucketname",
 				Prefix:      "",
@@ -193,7 +193,7 @@ var parseTests = []struct {
 	{
 		"s3://hostname.foo/bucketname",
 		Location{Scheme: "s3",
-			Config: s3.Config{
+			Config: &s3.Config{
 				Endpoint:    "hostname.foo",
 				Bucket:      "bucketname",
 				Prefix:      "",
@@ -204,7 +204,7 @@ var parseTests = []struct {
 	{
 		"s3://hostname.foo/bucketname/prefix/directory",
 		Location{Scheme: "s3",
-			Config: s3.Config{
+			Config: &s3.Config{
 				Endpoint:    "hostname.foo",
 				Bucket:      "bucketname",
 				Prefix:      "prefix/directory",
@@ -215,7 +215,7 @@ var parseTests = []struct {
 	{
 		"s3:eu-central-1/repo",
 		Location{Scheme: "s3",
-			Config: s3.Config{
+			Config: &s3.Config{
 				Endpoint:    "eu-central-1",
 				Bucket:      "repo",
 				Prefix:      "",
@@ -226,7 +226,7 @@ var parseTests = []struct {
 	{
 		"s3:eu-central-1/repo/prefix/directory",
 		Location{Scheme: "s3",
-			Config: s3.Config{
+			Config: &s3.Config{
 				Endpoint:    "eu-central-1",
 				Bucket:      "repo",
 				Prefix:      "prefix/directory",
@@ -237,7 +237,7 @@ var parseTests = []struct {
 	{
 		"s3:https://hostname.foo/repo",
 		Location{Scheme: "s3",
-			Config: s3.Config{
+			Config: &s3.Config{
 				Endpoint:    "hostname.foo",
 				Bucket:      "repo",
 				Prefix:      "",
@@ -248,7 +248,7 @@ var parseTests = []struct {
 	{
 		"s3:https://hostname.foo/repo/prefix/directory",
 		Location{Scheme: "s3",
-			Config: s3.Config{
+			Config: &s3.Config{
 				Endpoint:    "hostname.foo",
 				Bucket:      "repo",
 				Prefix:      "prefix/directory",
@@ -259,7 +259,7 @@ var parseTests = []struct {
 	{
 		"s3:http://hostname.foo/repo",
 		Location{Scheme: "s3",
-			Config: s3.Config{
+			Config: &s3.Config{
 				Endpoint:    "hostname.foo",
 				Bucket:      "repo",
 				Prefix:      "",
@@ -271,7 +271,7 @@ var parseTests = []struct {
 	{
 		"swift:container17:/",
 		Location{Scheme: "swift",
-			Config: swift.Config{
+			Config: &swift.Config{
 				Container:   "container17",
 				Prefix:      "",
 				Connections: 5,
@@ -281,7 +281,7 @@ var parseTests = []struct {
 	{
 		"swift:container17:/prefix97",
 		Location{Scheme: "swift",
-			Config: swift.Config{
+			Config: &swift.Config{
 				Container:   "container17",
 				Prefix:      "prefix97",
 				Connections: 5,
@@ -291,7 +291,7 @@ var parseTests = []struct {
 	{
 		"rest:http://hostname.foo:1234/",
 		Location{Scheme: "rest",
-			Config: rest.Config{
+			Config: &rest.Config{
 				URL:         parseURL("http://hostname.foo:1234/"),
 				Connections: 5,
 			},
@@ -299,7 +299,7 @@ var parseTests = []struct {
 	},
 	{
 		"b2:bucketname:/prefix", Location{Scheme: "b2",
-			Config: b2.Config{
+			Config: &b2.Config{
 				Bucket:      "bucketname",
 				Prefix:      "prefix",
 				Connections: 5,
@@ -308,7 +308,7 @@ var parseTests = []struct {
 	},
 	{
 		"b2:bucketname", Location{Scheme: "b2",
-			Config: b2.Config{
+			Config: &b2.Config{
 				Bucket:      "bucketname",
 				Prefix:      "",
 				Connections: 5,
diff --git a/internal/backend/mem/mem_backend_test.go b/internal/backend/mem/mem_backend_test.go
index 819c6a2b6..3dea089bc 100644
--- a/internal/backend/mem/mem_backend_test.go
+++ b/internal/backend/mem/mem_backend_test.go
@@ -15,19 +15,19 @@ type memConfig struct {
 	be restic.Backend
 }
 
-func newTestSuite() *test.Suite {
-	return &test.Suite{
+func newTestSuite() *test.Suite[*memConfig] {
+	return &test.Suite[*memConfig]{
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
-			return &memConfig{}, nil
+		NewConfig: func() (**memConfig, error) {
+			cfg := &memConfig{}
+			return &cfg, nil
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(cfg interface{}) (restic.Backend, error) {
-			c := cfg.(*memConfig)
-			if c.be != nil {
-				_, err := c.be.Stat(context.TODO(), restic.Handle{Type: restic.ConfigFile})
-				if err != nil && !c.be.IsNotExist(err) {
+		Create: func(cfg *memConfig) (restic.Backend, error) {
+			if cfg.be != nil {
+				_, err := cfg.be.Stat(context.TODO(), restic.Handle{Type: restic.ConfigFile})
+				if err != nil && !cfg.be.IsNotExist(err) {
 					return nil, err
 				}
 
@@ -36,21 +36,20 @@ func newTestSuite() *test.Suite {
 				}
 			}
 
-			c.be = mem.New()
-			return c.be, nil
+			cfg.be = mem.New()
+			return cfg.be, nil
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(cfg interface{}) (restic.Backend, error) {
-			c := cfg.(*memConfig)
-			if c.be == nil {
-				c.be = mem.New()
+		Open: func(cfg *memConfig) (restic.Backend, error) {
+			if cfg.be == nil {
+				cfg.be = mem.New()
 			}
-			return c.be, nil
+			return cfg.be, nil
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(cfg interface{}) error {
+		Cleanup: func(cfg *memConfig) error {
 			// no cleanup needed
 			return nil
 		},
diff --git a/internal/backend/rclone/backend_test.go b/internal/backend/rclone/backend_test.go
index 12fed6274..c497271f6 100644
--- a/internal/backend/rclone/backend_test.go
+++ b/internal/backend/rclone/backend_test.go
@@ -12,22 +12,21 @@ import (
 	rtest "github.com/restic/restic/internal/test"
 )
 
-func newTestSuite(t testing.TB) *test.Suite {
+func newTestSuite(t testing.TB) *test.Suite[rclone.Config] {
 	dir := rtest.TempDir(t)
 
-	return &test.Suite{
+	return &test.Suite[rclone.Config]{
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
+		NewConfig: func() (*rclone.Config, error) {
 			t.Logf("use backend at %v", dir)
 			cfg := rclone.NewConfig()
 			cfg.Remote = dir
-			return cfg, nil
+			return &cfg, nil
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
+		Create: func(cfg rclone.Config) (restic.Backend, error) {
 			t.Logf("Create()")
-			cfg := config.(rclone.Config)
 			be, err := rclone.Create(context.TODO(), cfg)
 			var e *exec.Error
 			if errors.As(err, &e) && e.Err == exec.ErrNotFound {
@@ -38,9 +37,8 @@ func newTestSuite(t testing.TB) *test.Suite {
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
+		Open: func(cfg rclone.Config) (restic.Backend, error) {
 			t.Logf("Open()")
-			cfg := config.(rclone.Config)
 			return rclone.Open(cfg, nil)
 		},
 	}
diff --git a/internal/backend/rclone/config.go b/internal/backend/rclone/config.go
index f8dc0d84d..2071d84e2 100644
--- a/internal/backend/rclone/config.go
+++ b/internal/backend/rclone/config.go
@@ -34,7 +34,7 @@ func NewConfig() Config {
 }
 
 // ParseConfig parses the string s and extracts the remote server URL.
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	if !strings.HasPrefix(s, "rclone:") {
 		return nil, errors.New("invalid rclone backend specification")
 	}
@@ -42,5 +42,5 @@ func ParseConfig(s string) (interface{}, error) {
 	s = s[7:]
 	cfg := NewConfig()
 	cfg.Remote = s
-	return cfg, nil
+	return &cfg, nil
 }
diff --git a/internal/backend/rclone/config_test.go b/internal/backend/rclone/config_test.go
index 923555136..67b983f66 100644
--- a/internal/backend/rclone/config_test.go
+++ b/internal/backend/rclone/config_test.go
@@ -1,37 +1,24 @@
 package rclone
 
 import (
-	"reflect"
 	"testing"
+
+	"github.com/restic/restic/internal/backend/test"
 )
 
-func TestParseConfig(t *testing.T) {
-	var tests = []struct {
-		s   string
-		cfg Config
-	}{
-		{
-			"rclone:local:foo:/bar",
-			Config{
-				Remote:      "local:foo:/bar",
-				Program:     defaultConfig.Program,
-				Args:        defaultConfig.Args,
-				Connections: defaultConfig.Connections,
-				Timeout:     defaultConfig.Timeout,
-			},
+var configTests = []test.ConfigTestData[Config]{
+	{
+		S: "rclone:local:foo:/bar",
+		Cfg: Config{
+			Remote:      "local:foo:/bar",
+			Program:     defaultConfig.Program,
+			Args:        defaultConfig.Args,
+			Connections: defaultConfig.Connections,
+			Timeout:     defaultConfig.Timeout,
 		},
-	}
-
-	for _, test := range tests {
-		t.Run("", func(t *testing.T) {
-			cfg, err := ParseConfig(test.s)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			if !reflect.DeepEqual(cfg, test.cfg) {
-				t.Fatalf("wrong config, want:\n  %v\ngot:\n  %v", test.cfg, cfg)
-			}
-		})
-	}
+	},
+}
+
+func TestParseConfig(t *testing.T) {
+	test.ParseConfigTester(t, ParseConfig, configTests)
 }
diff --git a/internal/backend/rest/config.go b/internal/backend/rest/config.go
index 388153fce..ba42a0220 100644
--- a/internal/backend/rest/config.go
+++ b/internal/backend/rest/config.go
@@ -26,7 +26,7 @@ func NewConfig() Config {
 }
 
 // ParseConfig parses the string s and extracts the REST server URL.
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	if !strings.HasPrefix(s, "rest:") {
 		return nil, errors.New("invalid REST backend specification")
 	}
@@ -40,7 +40,7 @@ func ParseConfig(s string) (interface{}, error) {
 
 	cfg := NewConfig()
 	cfg.URL = u
-	return cfg, nil
+	return &cfg, nil
 }
 
 // StripPassword removes the password from the URL
diff --git a/internal/backend/rest/config_test.go b/internal/backend/rest/config_test.go
index 2d8e32a73..8cfc78407 100644
--- a/internal/backend/rest/config_test.go
+++ b/internal/backend/rest/config_test.go
@@ -2,8 +2,9 @@ package rest
 
 import (
 	"net/url"
-	"reflect"
 	"testing"
+
+	"github.com/restic/restic/internal/backend/test"
 )
 
 func parseURL(s string) *url.URL {
@@ -15,20 +16,17 @@ func parseURL(s string) *url.URL {
 	return u
 }
 
-var configTests = []struct {
-	s   string
-	cfg Config
-}{
+var configTests = []test.ConfigTestData[Config]{
 	{
-		s: "rest:http://localhost:1234",
-		cfg: Config{
+		S: "rest:http://localhost:1234",
+		Cfg: Config{
 			URL:         parseURL("http://localhost:1234/"),
 			Connections: 5,
 		},
 	},
 	{
-		s: "rest:http://localhost:1234/",
-		cfg: Config{
+		S: "rest:http://localhost:1234/",
+		Cfg: Config{
 			URL:         parseURL("http://localhost:1234/"),
 			Connections: 5,
 		},
@@ -36,17 +34,5 @@ var configTests = []struct {
 }
 
 func TestParseConfig(t *testing.T) {
-	for _, test := range configTests {
-		t.Run("", func(t *testing.T) {
-			cfg, err := ParseConfig(test.s)
-			if err != nil {
-				t.Fatalf("%s failed: %v", test.s, err)
-			}
-
-			if !reflect.DeepEqual(cfg, test.cfg) {
-				t.Fatalf("\ninput: %s\n wrong config, want:\n  %v\ngot:\n  %v",
-					test.s, test.cfg, cfg)
-			}
-		})
-	}
+	test.ParseConfigTester(t, ParseConfig, configTests)
 }
diff --git a/internal/backend/rest/rest_test.go b/internal/backend/rest/rest_test.go
index 9d7073bc5..2ebd00f5e 100644
--- a/internal/backend/rest/rest_test.go
+++ b/internal/backend/rest/rest_test.go
@@ -67,36 +67,34 @@ func runRESTServer(ctx context.Context, t testing.TB, dir string) (*url.URL, fun
 	return url, cleanup
 }
 
-func newTestSuite(_ context.Context, t testing.TB, url *url.URL, minimalData bool) *test.Suite {
+func newTestSuite(_ context.Context, t testing.TB, url *url.URL, minimalData bool) *test.Suite[rest.Config] {
 	tr, err := backend.Transport(backend.TransportOptions{})
 	if err != nil {
 		t.Fatalf("cannot create transport for tests: %v", err)
 	}
 
-	return &test.Suite{
+	return &test.Suite[rest.Config]{
 		MinimalData: minimalData,
 
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
+		NewConfig: func() (*rest.Config, error) {
 			cfg := rest.NewConfig()
 			cfg.URL = url
-			return cfg, nil
+			return &cfg, nil
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(rest.Config)
+		Create: func(cfg rest.Config) (restic.Backend, error) {
 			return rest.Create(context.TODO(), cfg, tr)
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(rest.Config)
+		Open: func(cfg rest.Config) (restic.Backend, error) {
 			return rest.Open(cfg, tr)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
+		Cleanup: func(cfg rest.Config) error {
 			return nil
 		},
 	}
@@ -130,12 +128,10 @@ func TestBackendRESTExternalServer(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	c := cfg.(rest.Config)
-
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
-	newTestSuite(ctx, t, c.URL, true).RunTests(t)
+	newTestSuite(ctx, t, cfg.URL, true).RunTests(t)
 }
 
 func BenchmarkBackendREST(t *testing.B) {
diff --git a/internal/backend/s3/config.go b/internal/backend/s3/config.go
index 9050e20f4..525373d16 100644
--- a/internal/backend/s3/config.go
+++ b/internal/backend/s3/config.go
@@ -2,11 +2,13 @@ package s3
 
 import (
 	"net/url"
+	"os"
 	"path"
 	"strings"
 
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/options"
+	"github.com/restic/restic/internal/restic"
 )
 
 // Config contains all configuration necessary to connect to an s3 compatible
@@ -44,7 +46,7 @@ func init() {
 // supported configuration formats are s3://host/bucketname/prefix and
 // s3:host/bucketname/prefix. The host can also be a valid s3 region
 // name. If no prefix is given the prefix "restic" will be used.
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	switch {
 	case strings.HasPrefix(s, "s3:http"):
 		// assume that a URL has been specified, parse it and
@@ -75,7 +77,7 @@ func ParseConfig(s string) (interface{}, error) {
 	return createConfig(endpoint, bucket, prefix, false)
 }
 
-func createConfig(endpoint, bucket, prefix string, useHTTP bool) (interface{}, error) {
+func createConfig(endpoint, bucket, prefix string, useHTTP bool) (*Config, error) {
 	if endpoint == "" {
 		return nil, errors.New("s3: invalid format, host/region or bucket name not found")
 	}
@@ -89,5 +91,30 @@ func createConfig(endpoint, bucket, prefix string, useHTTP bool) (interface{}, e
 	cfg.UseHTTP = useHTTP
 	cfg.Bucket = bucket
 	cfg.Prefix = prefix
-	return cfg, nil
+	return &cfg, nil
+}
+
+var _ restic.ApplyEnvironmenter = &Config{}
+
+// ApplyEnvironment saves values from the environment to the config.
+func (cfg *Config) ApplyEnvironment(prefix string) error {
+	if cfg.KeyID == "" {
+		cfg.KeyID = os.Getenv(prefix + "AWS_ACCESS_KEY_ID")
+	}
+
+	if cfg.Secret.String() == "" {
+		cfg.Secret = options.NewSecretString(os.Getenv(prefix + "AWS_SECRET_ACCESS_KEY"))
+	}
+
+	if cfg.KeyID == "" && cfg.Secret.String() != "" {
+		return errors.Fatalf("unable to open S3 backend: Key ID ($AWS_ACCESS_KEY_ID) is empty")
+	} else if cfg.KeyID != "" && cfg.Secret.String() == "" {
+		return errors.Fatalf("unable to open S3 backend: Secret ($AWS_SECRET_ACCESS_KEY) is empty")
+	}
+
+	if cfg.Region == "" {
+		cfg.Region = os.Getenv(prefix + "AWS_DEFAULT_REGION")
+	}
+
+	return nil
 }
diff --git a/internal/backend/s3/config_test.go b/internal/backend/s3/config_test.go
index 821fbc244..21fbb27b9 100644
--- a/internal/backend/s3/config_test.go
+++ b/internal/backend/s3/config_test.go
@@ -3,94 +3,93 @@ package s3
 import (
 	"strings"
 	"testing"
+
+	"github.com/restic/restic/internal/backend/test"
 )
 
-var configTests = []struct {
-	s   string
-	cfg Config
-}{
-	{"s3://eu-central-1/bucketname", Config{
+var configTests = []test.ConfigTestData[Config]{
+	{S: "s3://eu-central-1/bucketname", Cfg: Config{
 		Endpoint:    "eu-central-1",
 		Bucket:      "bucketname",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"s3://eu-central-1/bucketname/", Config{
+	{S: "s3://eu-central-1/bucketname/", Cfg: Config{
 		Endpoint:    "eu-central-1",
 		Bucket:      "bucketname",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"s3://eu-central-1/bucketname/prefix/directory", Config{
+	{S: "s3://eu-central-1/bucketname/prefix/directory", Cfg: Config{
 		Endpoint:    "eu-central-1",
 		Bucket:      "bucketname",
 		Prefix:      "prefix/directory",
 		Connections: 5,
 	}},
-	{"s3://eu-central-1/bucketname/prefix/directory/", Config{
+	{S: "s3://eu-central-1/bucketname/prefix/directory/", Cfg: Config{
 		Endpoint:    "eu-central-1",
 		Bucket:      "bucketname",
 		Prefix:      "prefix/directory",
 		Connections: 5,
 	}},
-	{"s3:eu-central-1/foobar", Config{
+	{S: "s3:eu-central-1/foobar", Cfg: Config{
 		Endpoint:    "eu-central-1",
 		Bucket:      "foobar",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"s3:eu-central-1/foobar/", Config{
+	{S: "s3:eu-central-1/foobar/", Cfg: Config{
 		Endpoint:    "eu-central-1",
 		Bucket:      "foobar",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"s3:eu-central-1/foobar/prefix/directory", Config{
+	{S: "s3:eu-central-1/foobar/prefix/directory", Cfg: Config{
 		Endpoint:    "eu-central-1",
 		Bucket:      "foobar",
 		Prefix:      "prefix/directory",
 		Connections: 5,
 	}},
-	{"s3:eu-central-1/foobar/prefix/directory/", Config{
+	{S: "s3:eu-central-1/foobar/prefix/directory/", Cfg: Config{
 		Endpoint:    "eu-central-1",
 		Bucket:      "foobar",
 		Prefix:      "prefix/directory",
 		Connections: 5,
 	}},
-	{"s3:https://hostname:9999/foobar", Config{
+	{S: "s3:https://hostname:9999/foobar", Cfg: Config{
 		Endpoint:    "hostname:9999",
 		Bucket:      "foobar",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"s3:https://hostname:9999/foobar/", Config{
+	{S: "s3:https://hostname:9999/foobar/", Cfg: Config{
 		Endpoint:    "hostname:9999",
 		Bucket:      "foobar",
 		Prefix:      "",
 		Connections: 5,
 	}},
-	{"s3:http://hostname:9999/foobar", Config{
+	{S: "s3:http://hostname:9999/foobar", Cfg: Config{
 		Endpoint:    "hostname:9999",
 		Bucket:      "foobar",
 		Prefix:      "",
 		UseHTTP:     true,
 		Connections: 5,
 	}},
-	{"s3:http://hostname:9999/foobar/", Config{
+	{S: "s3:http://hostname:9999/foobar/", Cfg: Config{
 		Endpoint:    "hostname:9999",
 		Bucket:      "foobar",
 		Prefix:      "",
 		UseHTTP:     true,
 		Connections: 5,
 	}},
-	{"s3:http://hostname:9999/bucket/prefix/directory", Config{
+	{S: "s3:http://hostname:9999/bucket/prefix/directory", Cfg: Config{
 		Endpoint:    "hostname:9999",
 		Bucket:      "bucket",
 		Prefix:      "prefix/directory",
 		UseHTTP:     true,
 		Connections: 5,
 	}},
-	{"s3:http://hostname:9999/bucket/prefix/directory/", Config{
+	{S: "s3:http://hostname:9999/bucket/prefix/directory/", Cfg: Config{
 		Endpoint:    "hostname:9999",
 		Bucket:      "bucket",
 		Prefix:      "prefix/directory",
@@ -100,19 +99,7 @@ var configTests = []struct {
 }
 
 func TestParseConfig(t *testing.T) {
-	for i, test := range configTests {
-		cfg, err := ParseConfig(test.s)
-		if err != nil {
-			t.Errorf("test %d:%s failed: %v", i, test.s, err)
-			continue
-		}
-
-		if cfg != test.cfg {
-			t.Errorf("test %d:\ninput:\n  %s\n wrong config, want:\n  %v\ngot:\n  %v",
-				i, test.s, test.cfg, cfg)
-			continue
-		}
-	}
+	test.ParseConfigTester(t, ParseConfig, configTests)
 }
 
 func TestParseError(t *testing.T) {
diff --git a/internal/backend/s3/s3_test.go b/internal/backend/s3/s3_test.go
index c024251a9..1cdc6d7e9 100644
--- a/internal/backend/s3/s3_test.go
+++ b/internal/backend/s3/s3_test.go
@@ -120,15 +120,15 @@ func createS3(t testing.TB, cfg MinioTestConfig, tr http.RoundTripper) (be resti
 	return be, err
 }
 
-func newMinioTestSuite(ctx context.Context, t testing.TB) *test.Suite {
+func newMinioTestSuite(ctx context.Context, t testing.TB) *test.Suite[MinioTestConfig] {
 	tr, err := backend.Transport(backend.TransportOptions{})
 	if err != nil {
 		t.Fatalf("cannot create transport for tests: %v", err)
 	}
 
-	return &test.Suite{
+	return &test.Suite[MinioTestConfig]{
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
+		NewConfig: func() (*MinioTestConfig, error) {
 			cfg := MinioTestConfig{}
 
 			cfg.tempdir = rtest.TempDir(t)
@@ -142,13 +142,11 @@ func newMinioTestSuite(ctx context.Context, t testing.TB) *test.Suite {
 			cfg.Config.UseHTTP = true
 			cfg.Config.KeyID = key
 			cfg.Config.Secret = options.NewSecretString(secret)
-			return cfg, nil
+			return &cfg, nil
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(MinioTestConfig)
-
+		Create: func(cfg MinioTestConfig) (restic.Backend, error) {
 			be, err := createS3(t, cfg, tr)
 			if err != nil {
 				return nil, err
@@ -167,14 +165,12 @@ func newMinioTestSuite(ctx context.Context, t testing.TB) *test.Suite {
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(MinioTestConfig)
+		Open: func(cfg MinioTestConfig) (restic.Backend, error) {
 			return s3.Open(ctx, cfg.Config, tr)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
-			cfg := config.(MinioTestConfig)
+		Cleanup: func(cfg MinioTestConfig) error {
 			if cfg.stopServer != nil {
 				cfg.stopServer()
 			}
@@ -217,24 +213,23 @@ func BenchmarkBackendMinio(t *testing.B) {
 	newMinioTestSuite(ctx, t).RunBenchmarks(t)
 }
 
-func newS3TestSuite(t testing.TB) *test.Suite {
+func newS3TestSuite(t testing.TB) *test.Suite[s3.Config] {
 	tr, err := backend.Transport(backend.TransportOptions{})
 	if err != nil {
 		t.Fatalf("cannot create transport for tests: %v", err)
 	}
 
-	return &test.Suite{
+	return &test.Suite[s3.Config]{
 		// do not use excessive data
 		MinimalData: true,
 
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
-			s3cfg, err := s3.ParseConfig(os.Getenv("RESTIC_TEST_S3_REPOSITORY"))
+		NewConfig: func() (*s3.Config, error) {
+			cfg, err := s3.ParseConfig(os.Getenv("RESTIC_TEST_S3_REPOSITORY"))
 			if err != nil {
 				return nil, err
 			}
 
-			cfg := s3cfg.(s3.Config)
 			cfg.KeyID = os.Getenv("RESTIC_TEST_S3_KEY")
 			cfg.Secret = options.NewSecretString(os.Getenv("RESTIC_TEST_S3_SECRET"))
 			cfg.Prefix = fmt.Sprintf("test-%d", time.Now().UnixNano())
@@ -242,9 +237,7 @@ func newS3TestSuite(t testing.TB) *test.Suite {
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(s3.Config)
-
+		Create: func(cfg s3.Config) (restic.Backend, error) {
 			be, err := s3.Create(context.TODO(), cfg, tr)
 			if err != nil {
 				return nil, err
@@ -263,15 +256,12 @@ func newS3TestSuite(t testing.TB) *test.Suite {
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(s3.Config)
+		Open: func(cfg s3.Config) (restic.Backend, error) {
 			return s3.Open(context.TODO(), cfg, tr)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
-			cfg := config.(s3.Config)
-
+		Cleanup: func(cfg s3.Config) error {
 			be, err := s3.Open(context.TODO(), cfg, tr)
 			if err != nil {
 				return err
diff --git a/internal/backend/sftp/config.go b/internal/backend/sftp/config.go
index 1a7309de3..ed7c2cafa 100644
--- a/internal/backend/sftp/config.go
+++ b/internal/backend/sftp/config.go
@@ -35,7 +35,7 @@ func init() {
 // and sftp:user@host:directory.  The directory will be path Cleaned and can
 // be an absolute path if it starts with a '/' (e.g.
 // sftp://user@host//absolute and sftp:user@host:/absolute).
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	var user, host, port, dir string
 	switch {
 	case strings.HasPrefix(s, "sftp://"):
@@ -89,5 +89,5 @@ func ParseConfig(s string) (interface{}, error) {
 	cfg.Port = port
 	cfg.Path = p
 
-	return cfg, nil
+	return &cfg, nil
 }
diff --git a/internal/backend/sftp/config_test.go b/internal/backend/sftp/config_test.go
index 3772c038b..bf7fa9653 100644
--- a/internal/backend/sftp/config_test.go
+++ b/internal/backend/sftp/config_test.go
@@ -2,94 +2,81 @@ package sftp
 
 import (
 	"testing"
+
+	"github.com/restic/restic/internal/backend/test"
 )
 
-var configTests = []struct {
-	in  string
-	cfg Config
-}{
+var configTests = []test.ConfigTestData[Config]{
 	// first form, user specified sftp://user@host/dir
 	{
-		"sftp://user@host/dir/subdir",
-		Config{User: "user", Host: "host", Path: "dir/subdir", Connections: 5},
+		S:   "sftp://user@host/dir/subdir",
+		Cfg: Config{User: "user", Host: "host", Path: "dir/subdir", Connections: 5},
 	},
 	{
-		"sftp://host/dir/subdir",
-		Config{Host: "host", Path: "dir/subdir", Connections: 5},
+		S:   "sftp://host/dir/subdir",
+		Cfg: Config{Host: "host", Path: "dir/subdir", Connections: 5},
 	},
 	{
-		"sftp://host//dir/subdir",
-		Config{Host: "host", Path: "/dir/subdir", Connections: 5},
+		S:   "sftp://host//dir/subdir",
+		Cfg: Config{Host: "host", Path: "/dir/subdir", Connections: 5},
 	},
 	{
-		"sftp://host:10022//dir/subdir",
-		Config{Host: "host", Port: "10022", Path: "/dir/subdir", Connections: 5},
+		S:   "sftp://host:10022//dir/subdir",
+		Cfg: Config{Host: "host", Port: "10022", Path: "/dir/subdir", Connections: 5},
 	},
 	{
-		"sftp://user@host:10022//dir/subdir",
-		Config{User: "user", Host: "host", Port: "10022", Path: "/dir/subdir", Connections: 5},
+		S:   "sftp://user@host:10022//dir/subdir",
+		Cfg: Config{User: "user", Host: "host", Port: "10022", Path: "/dir/subdir", Connections: 5},
 	},
 	{
-		"sftp://user@host/dir/subdir/../other",
-		Config{User: "user", Host: "host", Path: "dir/other", Connections: 5},
+		S:   "sftp://user@host/dir/subdir/../other",
+		Cfg: Config{User: "user", Host: "host", Path: "dir/other", Connections: 5},
 	},
 	{
-		"sftp://user@host/dir///subdir",
-		Config{User: "user", Host: "host", Path: "dir/subdir", Connections: 5},
+		S:   "sftp://user@host/dir///subdir",
+		Cfg: Config{User: "user", Host: "host", Path: "dir/subdir", Connections: 5},
 	},
 
 	// IPv6 address.
 	{
-		"sftp://user@[::1]/dir",
-		Config{User: "user", Host: "::1", Path: "dir", Connections: 5},
+		S:   "sftp://user@[::1]/dir",
+		Cfg: Config{User: "user", Host: "::1", Path: "dir", Connections: 5},
 	},
 	// IPv6 address with port.
 	{
-		"sftp://user@[::1]:22/dir",
-		Config{User: "user", Host: "::1", Port: "22", Path: "dir", Connections: 5},
+		S:   "sftp://user@[::1]:22/dir",
+		Cfg: Config{User: "user", Host: "::1", Port: "22", Path: "dir", Connections: 5},
 	},
 
 	// second form, user specified sftp:user@host:/dir
 	{
-		"sftp:user@host:/dir/subdir",
-		Config{User: "user", Host: "host", Path: "/dir/subdir", Connections: 5},
+		S:   "sftp:user@host:/dir/subdir",
+		Cfg: Config{User: "user", Host: "host", Path: "/dir/subdir", Connections: 5},
 	},
 	{
-		"sftp:user@domain@host:/dir/subdir",
-		Config{User: "user@domain", Host: "host", Path: "/dir/subdir", Connections: 5},
+		S:   "sftp:user@domain@host:/dir/subdir",
+		Cfg: Config{User: "user@domain", Host: "host", Path: "/dir/subdir", Connections: 5},
 	},
 	{
-		"sftp:host:../dir/subdir",
-		Config{Host: "host", Path: "../dir/subdir", Connections: 5},
+		S:   "sftp:host:../dir/subdir",
+		Cfg: Config{Host: "host", Path: "../dir/subdir", Connections: 5},
 	},
 	{
-		"sftp:user@host:dir/subdir:suffix",
-		Config{User: "user", Host: "host", Path: "dir/subdir:suffix", Connections: 5},
+		S:   "sftp:user@host:dir/subdir:suffix",
+		Cfg: Config{User: "user", Host: "host", Path: "dir/subdir:suffix", Connections: 5},
 	},
 	{
-		"sftp:user@host:dir/subdir/../other",
-		Config{User: "user", Host: "host", Path: "dir/other", Connections: 5},
+		S:   "sftp:user@host:dir/subdir/../other",
+		Cfg: Config{User: "user", Host: "host", Path: "dir/other", Connections: 5},
 	},
 	{
-		"sftp:user@host:dir///subdir",
-		Config{User: "user", Host: "host", Path: "dir/subdir", Connections: 5},
+		S:   "sftp:user@host:dir///subdir",
+		Cfg: Config{User: "user", Host: "host", Path: "dir/subdir", Connections: 5},
 	},
 }
 
 func TestParseConfig(t *testing.T) {
-	for i, test := range configTests {
-		cfg, err := ParseConfig(test.in)
-		if err != nil {
-			t.Errorf("test %d:%s failed: %v", i, test.in, err)
-			continue
-		}
-
-		if cfg != test.cfg {
-			t.Errorf("test %d:\ninput:\n  %s\n wrong config, want:\n  %v\ngot:\n  %v",
-				i, test.in, test.cfg, cfg)
-			continue
-		}
-	}
+	test.ParseConfigTester(t, ParseConfig, configTests)
 }
 
 var configTestsInvalid = []string{
diff --git a/internal/backend/sftp/sftp_test.go b/internal/backend/sftp/sftp_test.go
index 0dbcd291c..98175ca26 100644
--- a/internal/backend/sftp/sftp_test.go
+++ b/internal/backend/sftp/sftp_test.go
@@ -29,10 +29,10 @@ func findSFTPServerBinary() string {
 
 var sftpServer = findSFTPServerBinary()
 
-func newTestSuite(t testing.TB) *test.Suite {
-	return &test.Suite{
+func newTestSuite(t testing.TB) *test.Suite[sftp.Config] {
+	return &test.Suite[sftp.Config]{
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
+		NewConfig: func() (*sftp.Config, error) {
 			dir, err := os.MkdirTemp(rtest.TestTempDir, "restic-test-sftp-")
 			if err != nil {
 				t.Fatal(err)
@@ -40,7 +40,7 @@ func newTestSuite(t testing.TB) *test.Suite {
 
 			t.Logf("create new backend at %v", dir)
 
-			cfg := sftp.Config{
+			cfg := &sftp.Config{
 				Path:        dir,
 				Command:     fmt.Sprintf("%q -e", sftpServer),
 				Connections: 5,
@@ -49,20 +49,17 @@ func newTestSuite(t testing.TB) *test.Suite {
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(sftp.Config)
+		Create: func(cfg sftp.Config) (restic.Backend, error) {
 			return sftp.Create(context.TODO(), cfg)
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(sftp.Config)
+		Open: func(cfg sftp.Config) (restic.Backend, error) {
 			return sftp.Open(context.TODO(), cfg)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
-			cfg := config.(sftp.Config)
+		Cleanup: func(cfg sftp.Config) error {
 			if !rtest.TestCleanupTempDirs {
 				t.Logf("leaving test backend dir at %v", cfg.Path)
 			}
diff --git a/internal/backend/smb/config.go b/internal/backend/smb/config.go
index d6f368b98..1d9f9d7ac 100644
--- a/internal/backend/smb/config.go
+++ b/internal/backend/smb/config.go
@@ -2,6 +2,7 @@ package smb
 
 import (
 	"net/url"
+	"os"
 	"path"
 	"strconv"
 	"strings"
@@ -9,6 +10,7 @@ import (
 
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/options"
+	"github.com/restic/restic/internal/restic"
 )
 
 // Config contains all configuration necessary to connect to an SMB server
@@ -54,7 +56,7 @@ func init() {
 // ParseConfig parses the string s and extracts the s3 config. The
 // supported configuration format is smb://[user@]host[:port]/sharename/directory.
 // User and port are optional. Default port is 445.
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	var repo string
 	switch {
 	case strings.HasPrefix(s, "smb://"):
@@ -106,7 +108,7 @@ func ParseConfig(s string) (interface{}, error) {
 	return createConfig(user, host, portNum, sharename, directory)
 }
 
-func createConfig(user string, host string, port int, sharename, directory string) (interface{}, error) {
+func createConfig(user string, host string, port int, sharename, directory string) (*Config, error) {
 	if host == "" {
 		return nil, errors.New("smb: invalid format, Host not found")
 	}
@@ -121,5 +123,26 @@ func createConfig(user string, host string, port int, sharename, directory strin
 	cfg.Port = port
 	cfg.ShareName = sharename
 	cfg.Path = directory
-	return cfg, nil
+	return &cfg, nil
+}
+
+var _ restic.ApplyEnvironmenter = &Config{}
+
+// ApplyEnvironment saves values from the environment to the config.
+func (cfg *Config) ApplyEnvironment(prefix string) error {
+	if cfg.User == "" {
+		cfg.User = os.Getenv("RESTIC_SMB_USER")
+	}
+
+	if cfg.Password.String() == "" {
+		cfg.Password = options.NewSecretString(os.Getenv("RESTIC_SMB_PASSWORD"))
+	}
+
+	if cfg.Domain == "" {
+		cfg.Domain = os.Getenv("RESTIC_SMB_DOMAIN")
+	}
+	if cfg.Domain == "" {
+		cfg.Domain = DefaultDomain
+	}
+	return nil
 }
diff --git a/internal/backend/smb/config_test.go b/internal/backend/smb/config_test.go
index 32f02c7bd..9b3e1dee2 100644
--- a/internal/backend/smb/config_test.go
+++ b/internal/backend/smb/config_test.go
@@ -3,76 +3,68 @@ package smb
 import (
 	"strings"
 	"testing"
+
+	"github.com/restic/restic/internal/backend/test"
 )
 
-var configTests = []struct {
-	s   string
-	cfg Config
-}{
-	{"smb://user@host/sharename/directory", Config{
-		Host:        "host",
-		Port:        DefaultSmbPort,
-		User:        "user",
-		Domain:      DefaultDomain,
-		ShareName:   "sharename",
-		Path:        "directory",
-		Connections: DefaultConnections,
-		IdleTimeout: DefaultIdleTimeout,
-	}},
-	{"smb://user@host:456/sharename/directory", Config{
-		Host:        "host",
-		Port:        456,
-		User:        "user",
-		Domain:      DefaultDomain,
-		ShareName:   "sharename",
-		Path:        "directory",
-		Connections: DefaultConnections,
-		IdleTimeout: DefaultIdleTimeout,
-	}},
-	{"smb://host/sharename/directory", Config{
-		Host:        "host",
-		Port:        DefaultSmbPort,
-		Domain:      DefaultDomain,
-		ShareName:   "sharename",
-		Path:        "directory",
-		Connections: DefaultConnections,
-		IdleTimeout: DefaultIdleTimeout,
-	}},
-	{"smb://host:446/sharename/directory", Config{
-		Host:        "host",
-		Port:        446,
-		Domain:      DefaultDomain,
-		ShareName:   "sharename",
-		Path:        "directory",
-		Connections: DefaultConnections,
-		IdleTimeout: DefaultIdleTimeout,
-	}},
-	{"smb:user@host:466/sharename/directory", Config{
-		Host:        "host",
-		Port:        466,
-		User:        "user",
-		Domain:      DefaultDomain,
-		ShareName:   "sharename",
-		Path:        "directory",
-		Connections: DefaultConnections,
-		IdleTimeout: DefaultIdleTimeout,
-	}},
+var configTests = []test.ConfigTestData[Config]{
+	{S: "smb://user@host/sharename/directory",
+		Cfg: Config{
+			Host:        "host",
+			Port:        DefaultSmbPort,
+			User:        "user",
+			Domain:      DefaultDomain,
+			ShareName:   "sharename",
+			Path:        "directory",
+			Connections: DefaultConnections,
+			IdleTimeout: DefaultIdleTimeout,
+		}},
+	{S: "smb://user@host:456/sharename/directory",
+		Cfg: Config{
+			Host:        "host",
+			Port:        456,
+			User:        "user",
+			Domain:      DefaultDomain,
+			ShareName:   "sharename",
+			Path:        "directory",
+			Connections: DefaultConnections,
+			IdleTimeout: DefaultIdleTimeout,
+		}},
+	{S: "smb://host/sharename/directory",
+		Cfg: Config{
+			Host:        "host",
+			Port:        DefaultSmbPort,
+			Domain:      DefaultDomain,
+			ShareName:   "sharename",
+			Path:        "directory",
+			Connections: DefaultConnections,
+			IdleTimeout: DefaultIdleTimeout,
+		}},
+	{S: "smb://host:446/sharename/directory",
+		Cfg: Config{
+			Host:        "host",
+			Port:        446,
+			Domain:      DefaultDomain,
+			ShareName:   "sharename",
+			Path:        "directory",
+			Connections: DefaultConnections,
+			IdleTimeout: DefaultIdleTimeout,
+		}},
+	{S: "smb:user@host:466/sharename/directory",
+		Cfg: Config{
+			Host:        "host",
+			Port:        466,
+			User:        "user",
+			Domain:      DefaultDomain,
+			ShareName:   "sharename",
+			Path:        "directory",
+			Connections: DefaultConnections,
+			IdleTimeout: DefaultIdleTimeout,
+		}},
 }
 
 func TestParseConfig(t *testing.T) {
-	for i, test := range configTests {
-		cfg, err := ParseConfig(test.s)
-		if err != nil {
-			t.Errorf("test %d:%s failed: %v", i, test.s, err)
-			continue
-		}
-
-		if cfg != test.cfg {
-			t.Errorf("test %d:\ninput:\n  %s\n wrong config, want:\n  %v\ngot:\n  %v",
-				i, test.s, test.cfg, cfg)
-			continue
-		}
-	}
+	test.ParseConfigTester(t, ParseConfig, configTests)
 }
 
 func TestParseError(t *testing.T) {
diff --git a/internal/backend/smb/smb_test.go b/internal/backend/smb/smb_test.go
index c210bb51b..2b81a5fbb 100644
--- a/internal/backend/smb/smb_test.go
+++ b/internal/backend/smb/smb_test.go
@@ -13,12 +13,12 @@ import (
 	rtest "github.com/restic/restic/internal/test"
 )
 
-func newTestSuite(t testing.TB) *test.Suite {
-	return &test.Suite{
+func newTestSuite(t testing.TB) *test.Suite[smb.Config] {
+	return &test.Suite[smb.Config]{
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
+		NewConfig: func() (*smb.Config, error) {
 
-			cfg := smb.NewConfig()
+			cfg := &smb.Config{}
 			cfg.Host = "127.0.0.1"
 			cfg.User = "smbuser"
 			cfg.ShareName = cfg.User
@@ -38,20 +38,17 @@ func newTestSuite(t testing.TB) *test.Suite {
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(smb.Config)
+		Create: func(cfg smb.Config) (restic.Backend, error) {
 			return smb.Create(context.TODO(), cfg)
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(smb.Config)
+		Open: func(cfg smb.Config) (restic.Backend, error) {
 			return smb.Open(context.TODO(), cfg)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
-			cfg := config.(smb.Config)
+		Cleanup: func(cfg smb.Config) error {
 			if !rtest.TestCleanupTempDirs {
 				t.Logf("leaving test backend dir at %v", cfg.Path)
 			}
diff --git a/internal/backend/swift/config.go b/internal/backend/swift/config.go
index ced256752..b9f5d3995 100644
--- a/internal/backend/swift/config.go
+++ b/internal/backend/swift/config.go
@@ -6,6 +6,7 @@ import (
 
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/options"
+	"github.com/restic/restic/internal/restic"
 )
 
 // Config contains basic configuration needed to specify swift location for a swift server
@@ -50,7 +51,7 @@ func NewConfig() Config {
 }
 
 // ParseConfig parses the string s and extract swift's container name and prefix.
-func ParseConfig(s string) (interface{}, error) {
+func ParseConfig(s string) (*Config, error) {
 	if !strings.HasPrefix(s, "swift:") {
 		return nil, errors.New("invalid URL, expected: swift:container-name:/[prefix]")
 	}
@@ -70,48 +71,49 @@ func ParseConfig(s string) (interface{}, error) {
 	cfg.Container = container
 	cfg.Prefix = prefix
 
-	return cfg, nil
+	return &cfg, nil
 }
 
+var _ restic.ApplyEnvironmenter = &Config{}
+
 // ApplyEnvironment saves values from the environment to the config.
-func ApplyEnvironment(prefix string, cfg interface{}) error {
-	c := cfg.(*Config)
+func (cfg *Config) ApplyEnvironment(prefix string) error {
 	for _, val := range []struct {
 		s   *string
 		env string
 	}{
 		// v2/v3 specific
-		{&c.UserName, prefix + "OS_USERNAME"},
-		{&c.APIKey, prefix + "OS_PASSWORD"},
-		{&c.Region, prefix + "OS_REGION_NAME"},
-		{&c.AuthURL, prefix + "OS_AUTH_URL"},
+		{&cfg.UserName, prefix + "OS_USERNAME"},
+		{&cfg.APIKey, prefix + "OS_PASSWORD"},
+		{&cfg.Region, prefix + "OS_REGION_NAME"},
+		{&cfg.AuthURL, prefix + "OS_AUTH_URL"},
 
 		// v3 specific
-		{&c.UserID, prefix + "OS_USER_ID"},
-		{&c.Domain, prefix + "OS_USER_DOMAIN_NAME"},
-		{&c.DomainID, prefix + "OS_USER_DOMAIN_ID"},
-		{&c.Tenant, prefix + "OS_PROJECT_NAME"},
-		{&c.TenantDomain, prefix + "OS_PROJECT_DOMAIN_NAME"},
-		{&c.TenantDomainID, prefix + "OS_PROJECT_DOMAIN_ID"},
-		{&c.TrustID, prefix + "OS_TRUST_ID"},
+		{&cfg.UserID, prefix + "OS_USER_ID"},
+		{&cfg.Domain, prefix + "OS_USER_DOMAIN_NAME"},
+		{&cfg.DomainID, prefix + "OS_USER_DOMAIN_ID"},
+		{&cfg.Tenant, prefix + "OS_PROJECT_NAME"},
+		{&cfg.TenantDomain, prefix + "OS_PROJECT_DOMAIN_NAME"},
+		{&cfg.TenantDomainID, prefix + "OS_PROJECT_DOMAIN_ID"},
+		{&cfg.TrustID, prefix + "OS_TRUST_ID"},
 
 		// v2 specific
-		{&c.TenantID, prefix + "OS_TENANT_ID"},
-		{&c.Tenant, prefix + "OS_TENANT_NAME"},
+		{&cfg.TenantID, prefix + "OS_TENANT_ID"},
+		{&cfg.Tenant, prefix + "OS_TENANT_NAME"},
 
 		// v1 specific
-		{&c.AuthURL, prefix + "ST_AUTH"},
-		{&c.UserName, prefix + "ST_USER"},
-		{&c.APIKey, prefix + "ST_KEY"},
+		{&cfg.AuthURL, prefix + "ST_AUTH"},
+		{&cfg.UserName, prefix + "ST_USER"},
+		{&cfg.APIKey, prefix + "ST_KEY"},
 
 		// Application Credential auth
-		{&c.ApplicationCredentialID, prefix + "OS_APPLICATION_CREDENTIAL_ID"},
-		{&c.ApplicationCredentialName, prefix + "OS_APPLICATION_CREDENTIAL_NAME"},
+		{&cfg.ApplicationCredentialID, prefix + "OS_APPLICATION_CREDENTIAL_ID"},
+		{&cfg.ApplicationCredentialName, prefix + "OS_APPLICATION_CREDENTIAL_NAME"},
 
 		// Manual authentication
-		{&c.StorageURL, prefix + "OS_STORAGE_URL"},
+		{&cfg.StorageURL, prefix + "OS_STORAGE_URL"},
 
-		{&c.DefaultContainerPolicy, prefix + "SWIFT_DEFAULT_CONTAINER_POLICY"},
+		{&cfg.DefaultContainerPolicy, prefix + "SWIFT_DEFAULT_CONTAINER_POLICY"},
 	} {
 		if *val.s == "" {
 			*val.s = os.Getenv(val.env)
@@ -121,8 +123,8 @@ func ApplyEnvironment(prefix string, cfg interface{}) error {
 		s   *options.SecretString
 		env string
 	}{
-		{&c.ApplicationCredentialSecret, prefix + "OS_APPLICATION_CREDENTIAL_SECRET"},
-		{&c.AuthToken, prefix + "OS_AUTH_TOKEN"},
+		{&cfg.ApplicationCredentialSecret, prefix + "OS_APPLICATION_CREDENTIAL_SECRET"},
+		{&cfg.AuthToken, prefix + "OS_AUTH_TOKEN"},
 	} {
 		if val.s.String() == "" {
 			*val.s = options.NewSecretString(os.Getenv(val.env))
diff --git a/internal/backend/swift/config_test.go b/internal/backend/swift/config_test.go
index 35f091a9b..3e094f9ea 100644
--- a/internal/backend/swift/config_test.go
+++ b/internal/backend/swift/config_test.go
@@ -1,29 +1,30 @@
 package swift
 
-import "testing"
+import (
+	"testing"
 
-var configTests = []struct {
-	s   string
-	cfg Config
-}{
+	"github.com/restic/restic/internal/backend/test"
+)
+
+var configTests = []test.ConfigTestData[Config]{
 	{
-		"swift:cnt1:/",
-		Config{
+		S: "swift:cnt1:/",
+		Cfg: Config{
 			Container:   "cnt1",
 			Prefix:      "",
 			Connections: 5,
 		},
 	},
 	{
-		"swift:cnt2:/prefix",
-		Config{Container: "cnt2",
+		S: "swift:cnt2:/prefix",
+		Cfg: Config{Container: "cnt2",
 			Prefix:      "prefix",
 			Connections: 5,
 		},
 	},
 	{
-		"swift:cnt3:/prefix/longer",
-		Config{Container: "cnt3",
+		S: "swift:cnt3:/prefix/longer",
+		Cfg: Config{Container: "cnt3",
 			Prefix:      "prefix/longer",
 			Connections: 5,
 		},
@@ -31,24 +32,7 @@ var configTests = []struct {
 }
 
 func TestParseConfig(t *testing.T) {
-	for _, test := range configTests {
-		t.Run("", func(t *testing.T) {
-			v, err := ParseConfig(test.s)
-			if err != nil {
-				t.Fatalf("parsing %q failed: %v", test.s, err)
-			}
-
-			cfg, ok := v.(Config)
-			if !ok {
-				t.Fatalf("wrong type returned, want Config, got %T", cfg)
-			}
-
-			if cfg != test.cfg {
-				t.Fatalf("wrong output for %q, want:\n  %#v\ngot:\n  %#v",
-					test.s, test.cfg, cfg)
-			}
-		})
-	}
+	test.ParseConfigTester(t, ParseConfig, configTests)
 }
 
 var configTestsInvalid = []string{
diff --git a/internal/backend/swift/swift_test.go b/internal/backend/swift/swift_test.go
index 0912e4f7e..cb0992010 100644
--- a/internal/backend/swift/swift_test.go
+++ b/internal/backend/swift/swift_test.go
@@ -15,13 +15,13 @@ import (
 	rtest "github.com/restic/restic/internal/test"
 )
 
-func newSwiftTestSuite(t testing.TB) *test.Suite {
+func newSwiftTestSuite(t testing.TB) *test.Suite[swift.Config] {
 	tr, err := backend.Transport(backend.TransportOptions{})
 	if err != nil {
 		t.Fatalf("cannot create transport for tests: %v", err)
 	}
 
-	return &test.Suite{
+	return &test.Suite[swift.Config]{
 		// do not use excessive data
 		MinimalData: true,
 
@@ -42,14 +42,13 @@ func newSwiftTestSuite(t testing.TB) *test.Suite {
 		},
 
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
-		NewConfig: func() (interface{}, error) {
-			swiftcfg, err := swift.ParseConfig(os.Getenv("RESTIC_TEST_SWIFT"))
+		NewConfig: func() (*swift.Config, error) {
+			cfg, err := swift.ParseConfig(os.Getenv("RESTIC_TEST_SWIFT"))
 			if err != nil {
 				return nil, err
 			}
 
-			cfg := swiftcfg.(swift.Config)
-			if err = swift.ApplyEnvironment("RESTIC_TEST_", &cfg); err != nil {
+			if err = cfg.ApplyEnvironment("RESTIC_TEST_"); err != nil {
 				return nil, err
 			}
 			cfg.Prefix += fmt.Sprintf("/test-%d", time.Now().UnixNano())
@@ -58,9 +57,7 @@ func newSwiftTestSuite(t testing.TB) *test.Suite {
 		},
 
 		// CreateFn is a function that creates a temporary repository for the tests.
-		Create: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(swift.Config)
-
+		Create: func(cfg swift.Config) (restic.Backend, error) {
 			be, err := swift.Open(context.TODO(), cfg, tr)
 			if err != nil {
 				return nil, err
@@ -79,15 +76,12 @@ func newSwiftTestSuite(t testing.TB) *test.Suite {
 		},
 
 		// OpenFn is a function that opens a previously created temporary repository.
-		Open: func(config interface{}) (restic.Backend, error) {
-			cfg := config.(swift.Config)
+		Open: func(cfg swift.Config) (restic.Backend, error) {
 			return swift.Open(context.TODO(), cfg, tr)
 		},
 
 		// CleanupFn removes data created during the tests.
-		Cleanup: func(config interface{}) error {
-			cfg := config.(swift.Config)
-
+		Cleanup: func(cfg swift.Config) error {
 			be, err := swift.Open(context.TODO(), cfg, tr)
 			if err != nil {
 				return err
diff --git a/internal/backend/test/benchmarks.go b/internal/backend/test/benchmarks.go
index b977eb682..150ef3987 100644
--- a/internal/backend/test/benchmarks.go
+++ b/internal/backend/test/benchmarks.go
@@ -29,7 +29,7 @@ func remove(t testing.TB, be restic.Backend, h restic.Handle) {
 
 // BenchmarkLoadFile benchmarks the Load() method of a backend by
 // loading a complete file.
-func (s *Suite) BenchmarkLoadFile(t *testing.B) {
+func (s *Suite[C]) BenchmarkLoadFile(t *testing.B) {
 	be := s.open(t)
 	defer s.close(t, be)
 
@@ -64,7 +64,7 @@ func (s *Suite) BenchmarkLoadFile(t *testing.B) {
 
 // BenchmarkLoadPartialFile benchmarks the Load() method of a backend by
 // loading the remainder of a file starting at a given offset.
-func (s *Suite) BenchmarkLoadPartialFile(t *testing.B) {
+func (s *Suite[C]) BenchmarkLoadPartialFile(t *testing.B) {
 	be := s.open(t)
 	defer s.close(t, be)
 
@@ -101,7 +101,7 @@ func (s *Suite) BenchmarkLoadPartialFile(t *testing.B) {
 
 // BenchmarkLoadPartialFileOffset benchmarks the Load() method of a
 // backend by loading a number of bytes of a file starting at a given offset.
-func (s *Suite) BenchmarkLoadPartialFileOffset(t *testing.B) {
+func (s *Suite[C]) BenchmarkLoadPartialFileOffset(t *testing.B) {
 	be := s.open(t)
 	defer s.close(t, be)
 
@@ -139,7 +139,7 @@ func (s *Suite) BenchmarkLoadPartialFileOffset(t *testing.B) {
 }
 
 // BenchmarkSave benchmarks the Save() method of a backend.
-func (s *Suite) BenchmarkSave(t *testing.B) {
+func (s *Suite[C]) BenchmarkSave(t *testing.B) {
 	be := s.open(t)
 	defer s.close(t, be)
 
diff --git a/internal/backend/test/config.go b/internal/backend/test/config.go
new file mode 100644
index 000000000..496ba2761
--- /dev/null
+++ b/internal/backend/test/config.go
@@ -0,0 +1,28 @@
+package test
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+type ConfigTestData[C comparable] struct {
+	S   string
+	Cfg C
+}
+
+func ParseConfigTester[C comparable](t *testing.T, parser func(s string) (*C, error), tests []ConfigTestData[C]) {
+	for i, test := range tests {
+		t.Run(fmt.Sprint(i), func(t *testing.T) {
+			cfg, err := parser(test.S)
+			if err != nil {
+				t.Fatalf("%s failed: %v", test.S, err)
+			}
+
+			if !reflect.DeepEqual(*cfg, test.Cfg) {
+				t.Fatalf("input: %s\n wrong config, want:\n  %#v\ngot:\n  %#v",
+					test.S, test.Cfg, *cfg)
+			}
+		})
+	}
+}
diff --git a/internal/backend/test/suite.go b/internal/backend/test/suite.go
index 45c6d96bd..75ae0630b 100644
--- a/internal/backend/test/suite.go
+++ b/internal/backend/test/suite.go
@@ -11,21 +11,21 @@ import (
 )
 
 // Suite implements a test suite for restic backends.
-type Suite struct {
+type Suite[C any] struct {
 	// Config should be used to configure the backend.
-	Config interface{}
+	Config *C
 
 	// NewConfig returns a config for a new temporary backend that will be used in tests.
-	NewConfig func() (interface{}, error)
+	NewConfig func() (*C, error)
 
 	// CreateFn is a function that creates a temporary repository for the tests.
-	Create func(cfg interface{}) (restic.Backend, error)
+	Create func(cfg C) (restic.Backend, error)
 
 	// OpenFn is a function that opens a previously created temporary repository.
-	Open func(cfg interface{}) (restic.Backend, error)
+	Open func(cfg C) (restic.Backend, error)
 
 	// CleanupFn removes data created during the tests.
-	Cleanup func(cfg interface{}) error
+	Cleanup func(cfg C) error
 
 	// MinimalData instructs the tests to not use excessive data.
 	MinimalData bool
@@ -40,7 +40,7 @@ type Suite struct {
 }
 
 // RunTests executes all defined tests as subtests of t.
-func (s *Suite) RunTests(t *testing.T) {
+func (s *Suite[C]) RunTests(t *testing.T) {
 	var err error
 	s.Config, err = s.NewConfig()
 	if err != nil {
@@ -61,7 +61,7 @@ func (s *Suite) RunTests(t *testing.T) {
 	}
 
 	if s.Cleanup != nil {
-		if err = s.Cleanup(s.Config); err != nil {
+		if err = s.Cleanup(*s.Config); err != nil {
 			t.Fatal(err)
 		}
 	}
@@ -72,7 +72,7 @@ type testFunction struct {
 	Fn   func(*testing.T)
 }
 
-func (s *Suite) testFuncs(t testing.TB) (funcs []testFunction) {
+func (s *Suite[C]) testFuncs(t testing.TB) (funcs []testFunction) {
 	tpe := reflect.TypeOf(s)
 	v := reflect.ValueOf(s)
 
@@ -107,7 +107,7 @@ type benchmarkFunction struct {
 	Fn   func(*testing.B)
 }
 
-func (s *Suite) benchmarkFuncs(t testing.TB) (funcs []benchmarkFunction) {
+func (s *Suite[C]) benchmarkFuncs(t testing.TB) (funcs []benchmarkFunction) {
 	tpe := reflect.TypeOf(s)
 	v := reflect.ValueOf(s)
 
@@ -138,7 +138,7 @@ func (s *Suite) benchmarkFuncs(t testing.TB) (funcs []benchmarkFunction) {
 }
 
 // RunBenchmarks executes all defined benchmarks as subtests of b.
-func (s *Suite) RunBenchmarks(b *testing.B) {
+func (s *Suite[C]) RunBenchmarks(b *testing.B) {
 	var err error
 	s.Config, err = s.NewConfig()
 	if err != nil {
@@ -158,28 +158,28 @@ func (s *Suite) RunBenchmarks(b *testing.B) {
 		return
 	}
 
-	if err = s.Cleanup(s.Config); err != nil {
+	if err = s.Cleanup(*s.Config); err != nil {
 		b.Fatal(err)
 	}
 }
 
-func (s *Suite) create(t testing.TB) restic.Backend {
-	be, err := s.Create(s.Config)
+func (s *Suite[C]) create(t testing.TB) restic.Backend {
+	be, err := s.Create(*s.Config)
 	if err != nil {
 		t.Fatal(err)
 	}
 	return be
 }
 
-func (s *Suite) open(t testing.TB) restic.Backend {
-	be, err := s.Open(s.Config)
+func (s *Suite[C]) open(t testing.TB) restic.Backend {
+	be, err := s.Open(*s.Config)
 	if err != nil {
 		t.Fatal(err)
 	}
 	return be
 }
 
-func (s *Suite) close(t testing.TB, be restic.Backend) {
+func (s *Suite[C]) close(t testing.TB, be restic.Backend) {
 	err := be.Close()
 	if err != nil {
 		t.Fatal(err)
diff --git a/internal/backend/test/tests.go b/internal/backend/test/tests.go
index a9514bf6b..c4462495f 100644
--- a/internal/backend/test/tests.go
+++ b/internal/backend/test/tests.go
@@ -38,7 +38,7 @@ func beTest(ctx context.Context, be restic.Backend, h restic.Handle) (bool, erro
 
 // TestCreateWithConfig tests that creating a backend in a location which already
 // has a config file fails.
-func (s *Suite) TestCreateWithConfig(t *testing.T) {
+func (s *Suite[C]) TestCreateWithConfig(t *testing.T) {
 	b := s.open(t)
 	defer s.close(t, b)
 
@@ -57,7 +57,7 @@ func (s *Suite) TestCreateWithConfig(t *testing.T) {
 	store(t, b, restic.ConfigFile, []byte("test config"))
 
 	// now create the backend again, this must fail
-	_, err = s.Create(s.Config)
+	_, err = s.Create(*s.Config)
 	if err == nil {
 		t.Fatalf("expected error not found for creating a backend with an existing config file")
 	}
@@ -70,7 +70,7 @@ func (s *Suite) TestCreateWithConfig(t *testing.T) {
 }
 
 // TestLocation tests that a location string is returned.
-func (s *Suite) TestLocation(t *testing.T) {
+func (s *Suite[C]) TestLocation(t *testing.T) {
 	b := s.open(t)
 	defer s.close(t, b)
 
@@ -81,7 +81,7 @@ func (s *Suite) TestLocation(t *testing.T) {
 }
 
 // TestConfig saves and loads a config from the backend.
-func (s *Suite) TestConfig(t *testing.T) {
+func (s *Suite[C]) TestConfig(t *testing.T) {
 	b := s.open(t)
 	defer s.close(t, b)
 
@@ -118,7 +118,7 @@ func (s *Suite) TestConfig(t *testing.T) {
 }
 
 // TestLoad tests the backend's Load function.
-func (s *Suite) TestLoad(t *testing.T) {
+func (s *Suite[C]) TestLoad(t *testing.T) {
 	seedRand(t)
 
 	b := s.open(t)
@@ -222,8 +222,12 @@ func (s *Suite) TestLoad(t *testing.T) {
 	test.OK(t, b.Remove(context.TODO(), handle))
 }
 
+type setter interface {
+	SetListMaxItems(int)
+}
+
 // TestList makes sure that the backend implements List() pagination correctly.
-func (s *Suite) TestList(t *testing.T) {
+func (s *Suite[C]) TestList(t *testing.T) {
 	seedRand(t)
 
 	numTestFiles := rand.Intn(20) + 20
@@ -269,10 +273,6 @@ func (s *Suite) TestList(t *testing.T) {
 		t.Run(fmt.Sprintf("max-%v", test.maxItems), func(t *testing.T) {
 			list2 := make(map[restic.ID]int64)
 
-			type setter interface {
-				SetListMaxItems(int)
-			}
-
 			if s, ok := b.(setter); ok {
 				t.Logf("setting max list items to %d", test.maxItems)
 				s.SetListMaxItems(test.maxItems)
@@ -326,7 +326,7 @@ func (s *Suite) TestList(t *testing.T) {
 }
 
 // TestListCancel tests that the context is respected and the error is returned by List.
-func (s *Suite) TestListCancel(t *testing.T) {
+func (s *Suite[C]) TestListCancel(t *testing.T) {
 	seedRand(t)
 
 	numTestFiles := 5
@@ -466,7 +466,7 @@ func (ec errorCloser) Rewind() error {
 }
 
 // TestSave tests saving data in the backend.
-func (s *Suite) TestSave(t *testing.T) {
+func (s *Suite[C]) TestSave(t *testing.T) {
 	seedRand(t)
 
 	b := s.open(t)
@@ -582,7 +582,7 @@ func (r *incompleteByteReader) Length() int64 {
 }
 
 // TestSaveError tests saving data in the backend.
-func (s *Suite) TestSaveError(t *testing.T) {
+func (s *Suite[C]) TestSaveError(t *testing.T) {
 	seedRand(t)
 
 	b := s.open(t)
@@ -621,7 +621,7 @@ func (b *wrongByteReader) Hash() []byte {
 }
 
 // TestSaveWrongHash tests that uploads with a wrong hash fail
-func (s *Suite) TestSaveWrongHash(t *testing.T) {
+func (s *Suite[C]) TestSaveWrongHash(t *testing.T) {
 	seedRand(t)
 
 	b := s.open(t)
@@ -679,7 +679,7 @@ func testLoad(b restic.Backend, h restic.Handle) error {
 	})
 }
 
-func (s *Suite) delayedRemove(t testing.TB, be restic.Backend, handles ...restic.Handle) error {
+func (s *Suite[C]) delayedRemove(t testing.TB, be restic.Backend, handles ...restic.Handle) error {
 	// Some backend (swift, I'm looking at you) may implement delayed
 	// removal of data. Let's wait a bit if this happens.
 
@@ -746,7 +746,7 @@ func delayedList(t testing.TB, b restic.Backend, tpe restic.FileType, max int, m
 }
 
 // TestBackend tests all functions of the backend.
-func (s *Suite) TestBackend(t *testing.T) {
+func (s *Suite[C]) TestBackend(t *testing.T) {
 	b := s.open(t)
 	defer s.close(t, b)
 
@@ -867,7 +867,7 @@ func (s *Suite) TestBackend(t *testing.T) {
 }
 
 // TestZZZDelete tests the Delete function. The name ensures that this test is executed last.
-func (s *Suite) TestZZZDelete(t *testing.T) {
+func (s *Suite[C]) TestZZZDelete(t *testing.T) {
 	if !test.TestCleanupTempDirs {
 		t.Skipf("not removing backend, TestCleanupTempDirs is false")
 	}
diff --git a/internal/restorer/preallocate_darwin.go b/internal/fs/preallocate_darwin.go
similarity index 87%
rename from internal/restorer/preallocate_darwin.go
rename to internal/fs/preallocate_darwin.go
index ae6e5ee3e..af46e971b 100644
--- a/internal/restorer/preallocate_darwin.go
+++ b/internal/fs/preallocate_darwin.go
@@ -1,4 +1,4 @@
-package restorer
+package fs
 
 import (
 	"os"
@@ -6,7 +6,7 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-func preallocateFile(wr *os.File, size int64) error {
+func PreallocateFile(wr *os.File, size int64) error {
 	// try contiguous first
 	fst := unix.Fstore_t{
 		Flags:   unix.F_ALLOCATECONTIG | unix.F_ALLOCATEALL,
diff --git a/internal/restorer/preallocate_linux.go b/internal/fs/preallocate_linux.go
similarity index 76%
rename from internal/restorer/preallocate_linux.go
rename to internal/fs/preallocate_linux.go
index dc73ddfe2..30b9e4644 100644
--- a/internal/restorer/preallocate_linux.go
+++ b/internal/fs/preallocate_linux.go
@@ -1,4 +1,4 @@
-package restorer
+package fs
 
 import (
 	"os"
@@ -6,7 +6,7 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-func preallocateFile(wr *os.File, size int64) error {
+func PreallocateFile(wr *os.File, size int64) error {
 	if size <= 0 {
 		return nil
 	}
diff --git a/internal/restorer/preallocate_other.go b/internal/fs/preallocate_other.go
similarity index 73%
rename from internal/restorer/preallocate_other.go
rename to internal/fs/preallocate_other.go
index f01757bf4..4fb44d421 100644
--- a/internal/restorer/preallocate_other.go
+++ b/internal/fs/preallocate_other.go
@@ -1,11 +1,11 @@
 //go:build !linux && !darwin
 // +build !linux,!darwin
 
-package restorer
+package fs
 
 import "os"
 
-func preallocateFile(wr *os.File, size int64) error {
+func PreallocateFile(wr *os.File, size int64) error {
 	// Maybe truncate can help?
 	// Windows: This calls SetEndOfFile which preallocates space on disk
 	return wr.Truncate(size)
diff --git a/internal/restorer/preallocate_test.go b/internal/fs/preallocate_test.go
similarity index 85%
rename from internal/restorer/preallocate_test.go
rename to internal/fs/preallocate_test.go
index 0cc2b3f5d..9dabd2f36 100644
--- a/internal/restorer/preallocate_test.go
+++ b/internal/fs/preallocate_test.go
@@ -1,4 +1,4 @@
-package restorer
+package fs
 
 import (
 	"os"
@@ -7,7 +7,6 @@ import (
 	"syscall"
 	"testing"
 
-	"github.com/restic/restic/internal/fs"
 	"github.com/restic/restic/internal/test"
 )
 
@@ -23,7 +22,7 @@ func TestPreallocate(t *testing.T) {
 				test.OK(t, wr.Close())
 			}()
 
-			err = preallocateFile(wr, i)
+			err = PreallocateFile(wr, i)
 			if err == syscall.ENOTSUP {
 				t.SkipNow()
 			}
@@ -32,7 +31,7 @@ func TestPreallocate(t *testing.T) {
 			fi, err := wr.Stat()
 			test.OK(t, err)
 
-			efi := fs.ExtendedStat(fi)
+			efi := ExtendedStat(fi)
 			test.Assert(t, efi.Size == i || efi.Blocks > 0, "Preallocated size of %v, got size %v block %v", i, efi.Size, efi.Blocks)
 		})
 	}
diff --git a/internal/restic/backend.go b/internal/restic/backend.go
index b01071132..b6653fcb4 100644
--- a/internal/restic/backend.go
+++ b/internal/restic/backend.go
@@ -80,3 +80,8 @@ type FileInfo struct {
 	Size int64
 	Name string
 }
+
+// ApplyEnvironmenter fills in a backend configuration from the environment
+type ApplyEnvironmenter interface {
+	ApplyEnvironment(prefix string) error
+}
diff --git a/internal/restorer/fileswriter.go b/internal/restorer/fileswriter.go
index 0a26101f4..589aa502a 100644
--- a/internal/restorer/fileswriter.go
+++ b/internal/restorer/fileswriter.go
@@ -6,6 +6,7 @@ import (
 
 	"github.com/cespare/xxhash/v2"
 	"github.com/restic/restic/internal/debug"
+	"github.com/restic/restic/internal/fs"
 )
 
 // writes blobs to target files.
@@ -72,7 +73,7 @@ func (w *filesWriter) writeToFile(path string, blob []byte, offset int64, create
 					return nil, err
 				}
 			} else {
-				err := preallocateFile(wr.File, createSize)
+				err := fs.PreallocateFile(wr.File, createSize)
 				if err != nil {
 					// Just log the preallocate error but don't let it cause the restore process to fail.
 					// Preallocate might return an error if the filesystem (implementation) does not
diff --git a/internal/ui/backup/progress.go b/internal/ui/backup/progress.go
index 8e15662a6..4362a8c83 100644
--- a/internal/ui/backup/progress.go
+++ b/internal/ui/backup/progress.go
@@ -43,7 +43,8 @@ type Progress struct {
 	progress.Updater
 	mu sync.Mutex
 
-	start time.Time
+	start     time.Time
+	estimator rateEstimator
 
 	scanStarted, scanFinished bool
 
@@ -60,6 +61,7 @@ func NewProgress(printer ProgressPrinter, interval time.Duration) *Progress {
 		start:        time.Now(),
 		currentFiles: make(map[string]struct{}),
 		printer:      printer,
+		estimator:    *newRateEstimator(time.Now()),
 	}
 	p.Updater = *progress.NewUpdater(interval, func(runtime time.Duration, final bool) {
 		if final {
@@ -73,9 +75,14 @@ func NewProgress(printer ProgressPrinter, interval time.Duration) *Progress {
 
 			var secondsRemaining uint64
 			if p.scanFinished {
-				secs := float64(runtime / time.Second)
-				todo := float64(p.total.Bytes - p.processed.Bytes)
-				secondsRemaining = uint64(secs / float64(p.processed.Bytes) * todo)
+				rate := p.estimator.rate(time.Now())
+				tooSlowCutoff := 1024.
+				if rate <= tooSlowCutoff {
+					secondsRemaining = 0
+				} else {
+					todo := float64(p.total.Bytes - p.processed.Bytes)
+					secondsRemaining = uint64(todo / rate)
+				}
 			}
 
 			p.printer.Update(p.total, p.processed, p.errors, p.currentFiles, p.start, secondsRemaining)
@@ -105,6 +112,7 @@ func (p *Progress) addProcessed(c Counter) {
 	p.processed.Files += c.Files
 	p.processed.Dirs += c.Dirs
 	p.processed.Bytes += c.Bytes
+	p.estimator.recordBytes(time.Now(), c.Bytes)
 	p.scanStarted = true
 }
 
diff --git a/internal/ui/backup/rate_estimator.go b/internal/ui/backup/rate_estimator.go
new file mode 100644
index 000000000..5291fbae1
--- /dev/null
+++ b/internal/ui/backup/rate_estimator.go
@@ -0,0 +1,98 @@
+package backup
+
+import (
+	"container/list"
+	"time"
+)
+
+// rateBucket represents a one second window of recorded progress.
+type rateBucket struct {
+	totalBytes uint64
+	end        time.Time // the end of the time window, exclusive
+}
+
+// rateEstimator represents an estimate of the time to complete an operation.
+type rateEstimator struct {
+	buckets    *list.List
+	start      time.Time
+	totalBytes uint64
+}
+
+// newRateEstimator returns an estimator initialized to a presumed start time.
+func newRateEstimator(start time.Time) *rateEstimator {
+	return &rateEstimator{buckets: list.New(), start: start}
+}
+
+// See trim(), below.
+const (
+	bucketWidth             = time.Second
+	minRateEstimatorBytes   = 100 * 1000 * 1000
+	minRateEstimatorBuckets = 20
+	minRateEstimatorMinutes = 2
+)
+
+// trim removes the oldest history from the estimator assuming a given
+// current time.
+func (r *rateEstimator) trim(now time.Time) {
+	// The estimator retains byte transfer counts over a two minute window.
+	// However, to avoid removing too much history when transfer rates are
+	// low, the estimator also retains a minimum number of processed bytes
+	// across a minimum number of buckets. An operation that is processing a
+	// significant number of bytes per second will typically retain only a
+	// two minute window's worth of information. One that is making slow
+	// progress, such as one being over a rate limited connection, typically
+	// observes bursts of updates as infrequently as every ten or twenty
+	// seconds, in which case the other limiters will kick in. This heuristic
+	// avoids wildly fluctuating estimates over rate limited connections.
+	start := now.Add(-minRateEstimatorMinutes * time.Minute)
+
+	for e := r.buckets.Front(); e != nil; e = r.buckets.Front() {
+		if r.buckets.Len() <= minRateEstimatorBuckets {
+			break
+		}
+		b := e.Value.(*rateBucket)
+		if b.end.After(start) {
+			break
+		}
+		total := r.totalBytes - b.totalBytes
+		if total < minRateEstimatorBytes {
+			break
+		}
+		r.start = b.end
+		r.totalBytes = total
+		r.buckets.Remove(e)
+	}
+}
+
+// recordBytes records the transfer of a number of bytes at a given
+// time. Times passed in successive calls should advance monotonically (as
+// is the case with time.Now().
+func (r *rateEstimator) recordBytes(now time.Time, bytes uint64) {
+	if bytes == 0 {
+		return
+	}
+	var tail *rateBucket
+	if r.buckets.Len() > 0 {
+		tail = r.buckets.Back().Value.(*rateBucket)
+	}
+	if tail == nil || !tail.end.After(now) {
+		// The new bucket holds measurements in the time range [now .. now+1sec).
+		tail = &rateBucket{end: now.Add(bucketWidth)}
+		r.buckets.PushBack(tail)
+	}
+	tail.totalBytes += bytes
+	r.totalBytes += bytes
+	r.trim(now)
+}
+
+// rate returns an estimated bytes per second rate at a given time, or zero
+// if there is not enough data to compute a rate.
+func (r *rateEstimator) rate(now time.Time) float64 {
+	r.trim(now)
+	if !r.start.Before(now) {
+		return 0
+	}
+	elapsed := float64(now.Sub(r.start)) / float64(time.Second)
+	rate := float64(r.totalBytes) / elapsed
+	return rate
+}
diff --git a/internal/ui/backup/rate_estimator_test.go b/internal/ui/backup/rate_estimator_test.go
new file mode 100644
index 000000000..0ebc6972b
--- /dev/null
+++ b/internal/ui/backup/rate_estimator_test.go
@@ -0,0 +1,213 @@
+package backup
+
+import (
+	"fmt"
+	"math"
+	"testing"
+	"time"
+
+	rtest "github.com/restic/restic/internal/test"
+)
+
+const float64EqualityThreshold = 1e-6
+
+func almostEqual(a, b float64) bool {
+	if math.IsNaN(a) || math.IsNaN(b) {
+		panic("almostEqual passed a NaN")
+	}
+	return math.Abs(a-b) <= float64EqualityThreshold
+}
+
+func TestEstimatorDefault(t *testing.T) {
+	var start time.Time
+	e := newRateEstimator(start)
+	r := e.rate(start)
+	rtest.Assert(t, r == 0, "e.Rate == %v, want zero", r)
+	r = e.rate(start.Add(time.Hour))
+	rtest.Assert(t, r == 0, "e.Rate == %v, want zero", r)
+}
+
+func TestEstimatorSimple(t *testing.T) {
+	var start time.Time
+	type testcase struct {
+		bytes uint64
+		when  time.Duration
+		rate  float64
+	}
+
+	cases := []testcase{
+		{0, 0, 0},
+		{1, time.Second, 1},
+		{60, time.Second, 60},
+		{60, time.Minute, 1},
+	}
+	for _, c := range cases {
+		name := fmt.Sprintf("%+v", c)
+		t.Run(name, func(t *testing.T) {
+			e := newRateEstimator(start)
+			e.recordBytes(start.Add(time.Second), c.bytes)
+			rate := e.rate(start.Add(c.when))
+			rtest.Assert(t, almostEqual(rate, c.rate), "e.Rate == %v, want %v", rate, c.rate)
+		})
+	}
+}
+
+func TestBucketWidth(t *testing.T) {
+	var when time.Time
+
+	// Recording byte transfers within a bucket width's time window uses one
+	// bucket.
+	e := newRateEstimator(when)
+	e.recordBytes(when, 1)
+	e.recordBytes(when.Add(bucketWidth-time.Nanosecond), 1)
+	rtest.Assert(t, e.buckets.Len() == 1, "e.buckets.Len() is %d, want 1", e.buckets.Len())
+
+	b := e.buckets.Back().Value.(*rateBucket)
+	rtest.Assert(t, b.totalBytes == 2, "b.totalBytes is %d, want 2", b.totalBytes)
+	rtest.Assert(t, b.end == when.Add(bucketWidth), "b.end is %v, want %v", b.end, when.Add(bucketWidth))
+
+	// Recording a byte outside the bucket width causes another bucket.
+	e.recordBytes(when.Add(bucketWidth), 1)
+	rtest.Assert(t, e.buckets.Len() == 2, "e.buckets.Len() is %d, want 2", e.buckets.Len())
+
+	b = e.buckets.Back().Value.(*rateBucket)
+	rtest.Assert(t, b.totalBytes == 1, "b.totalBytes is %d, want 1", b.totalBytes)
+	rtest.Assert(t, b.end == when.Add(2*bucketWidth), "b.end is %v, want %v", b.end, when.Add(bucketWidth))
+
+	// Recording a byte after a longer delay creates a sparse bucket list.
+	e.recordBytes(when.Add(time.Hour+time.Millisecond), 7)
+	rtest.Assert(t, e.buckets.Len() == 3, "e.buckets.Len() is %d, want 3", e.buckets.Len())
+
+	b = e.buckets.Back().Value.(*rateBucket)
+	rtest.Assert(t, b.totalBytes == 7, "b.totalBytes is %d, want 7", b.totalBytes)
+	rtest.Equals(t, when.Add(time.Hour+time.Millisecond+time.Second), b.end)
+}
+
+type chunk struct {
+	repetitions uint64 // repetition count
+	bytes       uint64 // byte count (every second)
+}
+
+func applyChunks(chunks []chunk, t time.Time, e *rateEstimator) time.Time {
+	for _, c := range chunks {
+		for i := uint64(0); i < c.repetitions; i++ {
+			e.recordBytes(t, c.bytes)
+			t = t.Add(time.Second)
+		}
+	}
+	return t
+}
+
+func TestEstimatorResponsiveness(t *testing.T) {
+	type testcase struct {
+		description string
+		chunks      []chunk
+		rate        float64
+	}
+
+	cases := []testcase{
+		{
+			"1000 bytes/sec over one second",
+			[]chunk{
+				{1, 1000},
+			},
+			1000,
+		},
+		{
+			"1000 bytes/sec over one minute",
+			[]chunk{
+				{60, 1000},
+			},
+			1000,
+		},
+		{
+			"1000 bytes/sec for 10 seconds, then 2000 bytes/sec for 10 seconds",
+			[]chunk{
+				{10, 1000},
+				{10, 2000},
+			},
+			1500,
+		},
+		{
+			"1000 bytes/sec for one minute, then 2000 bytes/sec for one minute",
+			[]chunk{
+				{60, 1000},
+				{60, 2000},
+			},
+			1500,
+		},
+		{
+			"rate doubles after 30 seconds",
+			[]chunk{
+				{30, minRateEstimatorBytes},
+				{90, 2 * minRateEstimatorBytes},
+			},
+			minRateEstimatorBytes * 1.75,
+		},
+		{
+			"rate doubles after 31 seconds",
+			[]chunk{
+				{31, minRateEstimatorBytes},
+				{90, 2 * minRateEstimatorBytes},
+			},
+			// The expected rate is the same as the prior test case because the
+			// first second has rolled off the estimator.
+			minRateEstimatorBytes * 1.75,
+		},
+		{
+			"rate doubles after 90 seconds",
+			[]chunk{
+				{90, minRateEstimatorBytes},
+				{90, 2 * minRateEstimatorBytes},
+			},
+			// The expected rate is the same as the prior test case because the
+			// first 60 seconds have rolled off the estimator.
+			minRateEstimatorBytes * 1.75,
+		},
+		{
+			"rate doubles for two full minutes",
+			[]chunk{
+				{60, minRateEstimatorBytes},
+				{120, 2 * minRateEstimatorBytes},
+			},
+			2 * minRateEstimatorBytes,
+		},
+		{
+			"rate falls to zero",
+			[]chunk{
+				{30, minRateEstimatorBytes},
+				{30, 0},
+			},
+			minRateEstimatorBytes / 2,
+		},
+		{
+			"rate falls to zero for extended time",
+			[]chunk{
+				{60, 1000},
+				{300, 0},
+			},
+			1000 * 60 / (60 + 300.0),
+		},
+		{
+			"rate falls to zero for extended time (from high rate)",
+			[]chunk{
+				{2 * minRateEstimatorBuckets, minRateEstimatorBytes},
+				{300, 0},
+			},
+			// Expect that only minRateEstimatorBuckets buckets are used in the
+			// rate estimate.
+			minRateEstimatorBytes * minRateEstimatorBuckets /
+				(minRateEstimatorBuckets + 300.0),
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.description, func(t *testing.T) {
+			var w time.Time
+			e := newRateEstimator(w)
+			w = applyChunks(c.chunks, w, e)
+			r := e.rate(w)
+			rtest.Assert(t, almostEqual(r, c.rate), "e.Rate == %f, want %f", r, c.rate)
+		})
+	}
+}