diff --git a/include/villas/hook_list.hpp b/include/villas/hook_list.hpp
index 178d04773..9c00fbc8f 100644
--- a/include/villas/hook_list.hpp
+++ b/include/villas/hook_list.hpp
@@ -65,7 +65,7 @@ int hook_list_prepare_signals(struct vlist *hs, struct vlist *signals);
 
 int hook_list_add(struct vlist *hs, int mask, struct vpath *p, struct vnode *n);
 
-int hook_list_process(struct vlist *hs, struct sample * smps[], unsigned cnt);
+int hook_list_process(struct vlist *hs, struct sample * smps[], unsigned cnt, bool clone_if_modified = false);
 
 void hook_list_periodic(struct vlist *hs);
 
diff --git a/include/villas/node.h b/include/villas/node.h
index 396ee6fd4..f4b35dc1b 100644
--- a/include/villas/node.h
+++ b/include/villas/node.h
@@ -200,7 +200,7 @@ int node_reverse(struct vnode *n);
 
 int node_read(struct vnode *n, struct sample * smps[], unsigned cnt);
 
-int node_write(struct vnode *n, struct sample * smps[], unsigned cnt);
+int node_write(struct vnode *n, struct sample * smps[], unsigned cnt, bool clone_if_modified = false);
 
 int node_poll_fds(struct vnode *n, int fds[]);
 
diff --git a/lib/hook_list.cpp b/lib/hook_list.cpp
index 93dfe4604..c42eeac46 100644
--- a/lib/hook_list.cpp
+++ b/lib/hook_list.cpp
@@ -135,18 +135,27 @@ void hook_list_prepare(struct vlist *hs, vlist *sigs, int m, struct vpath *p, st
 	}
 }
 
-int hook_list_process(struct vlist *hs, struct sample * smps[], unsigned cnt)
+int hook_list_process(struct vlist *hs, struct sample *smps[], unsigned cnt, bool clone_if_modified)
 {
-	unsigned current, processed = 0;
+	unsigned processed = 0;
 
 	if (vlist_length(hs) == 0)
 		return cnt;
 
-	for (current = 0; current < cnt; current++) {
-		struct sample *smp = smps[current];
+	for (unsigned i = 0; i < cnt; i++) {
+		struct sample *smp, *old_smp;
 
-		for (size_t i = 0; i < vlist_length(hs); i++) {
-			Hook *h = (Hook *) vlist_at(hs, i);
+		if (clone_if_modified) {
+			old_smp = smps[i];
+			smps[i] = sample_clone(old_smp);
+
+			sample_decref(old_smp);
+		}
+
+		smp = smps[i];
+
+		for (size_t j = 0; j < vlist_length(hs); j++) {
+			Hook *h = (Hook *) vlist_at(hs, j);
 
 			auto ret = h->process(smp);
 			smp->signals = h->getSignals();
@@ -165,7 +174,7 @@ int hook_list_process(struct vlist *hs, struct sample * smps[], unsigned cnt)
 			}
 		}
 
-stop:	SWAP(smps[processed], smps[current]);
+stop:		SWAP(smps[processed], smps[i]);
 		processed++;
 skip: {}
 	}
diff --git a/lib/node.cpp b/lib/node.cpp
index a8fc2a0b9..8d55d54ea 100644
--- a/lib/node.cpp
+++ b/lib/node.cpp
@@ -494,7 +494,7 @@ int node_read(struct vnode *n, struct sample * smps[], unsigned cnt)
 #endif /* WITH_HOOKS */
 }
 
-int node_write(struct vnode *n, struct sample * smps[], unsigned cnt)
+int node_write(struct vnode *n, struct sample * smps[], unsigned cnt, bool clone_if_modified)
 {
 	int tosend, sent, nsent = 0;
 	unsigned vect;
@@ -508,7 +508,7 @@ int node_write(struct vnode *n, struct sample * smps[], unsigned cnt)
 
 #ifdef WITH_HOOKS
 	/* Run write hooks */
-	cnt = hook_list_process(&n->out.hooks, smps, cnt);
+	cnt = hook_list_process(&n->out.hooks, smps, cnt, clone_if_modified && !n->out.read_only_hooks);
 	if (cnt <= 0)
 		return cnt;
 #endif /* WITH_HOOKS */
diff --git a/lib/node_direction.cpp b/lib/node_direction.cpp
index 9f34090cb..0f33999b9 100644
--- a/lib/node_direction.cpp
+++ b/lib/node_direction.cpp
@@ -42,6 +42,8 @@ int node_direction_prepare(struct vnode_direction *nd, struct vnode *n)
 	int m = nd->builtin ? t | (int) Hook::Flags::BUILTIN : 0;
 
 	hook_list_prepare(&nd->hooks, &nd->signals, m, nullptr, n);
+
+	nd->read_only_hooks = hook_list_is_read_only(&nd->hooks);
 #endif /* WITH_HOOKS */
 
 	nd->state = State::PREPARED;
@@ -58,6 +60,7 @@ int node_direction_init(struct vnode_direction *nd, enum NodeDir dir, struct vno
 	nd->vectorize = 1;
 	nd->builtin = 1;
 	nd->path = nullptr;
+	nd->read_only_hooks = false;
 
 #ifdef WITH_HOOKS
 	ret = hook_list_init(&nd->hooks);