diff --git a/mars_client.c b/mars_client.c
index a5af1954..247b5e51 100644
--- a/mars_client.c
+++ b/mars_client.c
@@ -357,10 +357,26 @@ int receiver_thread(void *data)
 	return status;
 }
 
+static
+void _do_resubmit(struct client_output *output)
+{
+	if (!list_empty(&output->wait_list)) {
+		struct list_head *first = output->wait_list.next;
+		struct list_head *last = output->wait_list.prev;
+		struct list_head *old_start = output->mref_list.next;
+#define list_connect __list_del // the original routine has a misleading name: in reality it is more general
+		list_connect(&output->mref_list, first);
+		list_connect(last, old_start);
+		INIT_LIST_HEAD(&output->wait_list);
+		MARS_IO("done re-submit %p %p\n", first, last);
+	}
+}
+
 static int sender_thread(void *data)
 {
 	struct client_output *output = data;
 	struct client_brick *brick = output->brick;
+	unsigned long flags;
 	int status = 0;
 
 	output->receiver.restart_count = 0;
@@ -369,7 +385,6 @@ static int sender_thread(void *data)
 		struct list_head *tmp;
 		struct client_mref_aspect *mref_a;
 		struct mref_object *mref;
-		unsigned long flags;
 		bool do_resubmit = false;
 
 		if (unlikely(!output->socket)) {
@@ -387,20 +402,11 @@ static int sender_thread(void *data)
 			 */
 			MARS_IO("re-submit\n");
 			traced_lock(&output->lock, flags);
-			if (!list_empty(&output->wait_list)) {
-				struct list_head *first = output->wait_list.next;
-				struct list_head *last = output->wait_list.prev;
-				struct list_head *old_start = output->mref_list.next;
-#define list_connect __list_del // the original routine has a misleading name: in reality it is more general
-				list_connect(&output->mref_list, first);
-				list_connect(last, old_start);
-				INIT_LIST_HEAD(&output->wait_list);
-				MARS_IO("done re-submit %p %p\n", first, last);
-			}
+			_do_resubmit(output);
 			traced_unlock(&output->lock, flags);
 		}
 
-		wait_event_interruptible_timeout(output->event, !list_empty(&output->mref_list) || output->get_info, 10 * HZ);
+		wait_event_interruptible_timeout(output->event, !list_empty(&output->mref_list) || output->get_info || kthread_should_stop(), 1 * HZ);
 		
 		if (output->get_info) {
 			status = _request_info(output);
@@ -446,8 +452,33 @@ static int sender_thread(void *data)
 
 	_kill_socket(output);
 
+	/* Signal error on all pending IO requests.
+	 * We have no other chance (except probably delaying
+	 * this until destruction which mostly is not what
+	 * we want).
+	 */
+	traced_lock(&output->lock, flags);
+	_do_resubmit(output);
+	while (!list_empty(&output->mref_list)) {
+		struct list_head *tmp = output->mref_list.next;
+		struct client_mref_aspect *mref_a;
+		struct mref_object *mref;
+
+		list_del_init(tmp);
+		traced_unlock(&output->lock, flags);
+		mref_a = container_of(tmp, struct client_mref_aspect, io_head);
+		mref = mref_a->object;
+		MARS_DBG("signalling IO error at pos = %lld len = %d\n", mref->ref_pos, mref->ref_len);
+		atomic_dec(&output->fly_count);
+		SIMPLE_CALLBACK(mref, -ENOTCONN);
+		client_ref_put(output, mref);
+		traced_lock(&output->lock, flags);
+	}
+	traced_unlock(&output->lock, flags);
+
 	output->sender.terminated = true;
 	wake_up_interruptible(&output->sender.run_event);
+	MARS_DBG("sender terminated\n");
 	return status;
 }
 
diff --git a/mars_copy.c b/mars_copy.c
index 14b824e9..f76f2f08 100644
--- a/mars_copy.c
+++ b/mars_copy.c
@@ -372,13 +372,13 @@ done:
 }
 
 static
-void _run_copy(struct copy_brick *brick)
+int _run_copy(struct copy_brick *brick)
 {
 	int max;
 	loff_t pos;
 	loff_t limit = 0;
 	short prev;
-	int status;
+	int res_status = 0;
 
 	if (unlikely(_clear_clash(brick))) {
 		int i;
@@ -389,7 +389,7 @@ void _run_copy(struct copy_brick *brick)
 			_clash(brick);
 			MARS_DBG("re-clash\n");
 			msleep(100);
-			return;
+			return 0;
 		}
 		for (i = 0; i < MAX_COPY_PARA; i++) {
 			_clear_mref(brick, i, 0);
@@ -416,7 +416,9 @@ void _run_copy(struct copy_brick *brick)
 		prev = index;
 		// call the finite state automaton
 		if (!st->active[0] && !st->active[1]) {
+			int status;
 			status = _next_state(brick, index, pos);
+			MARS_IO("index = %d pos = %lld status 0 %d\n", index, pos, status);
 			limit = pos;
 		}
 	}
@@ -432,6 +434,7 @@ void _run_copy(struct copy_brick *brick)
 			}
 			st->state = COPY_STATE_START;
 			if (unlikely(st->error < 0)) {
+				res_status = st->error;
 				break;
 			}
 			count += st->len;
@@ -446,6 +449,7 @@ void _run_copy(struct copy_brick *brick)
 			_update_percent(brick);
 		}
 	}
+	return res_status;
 }
 
 static int _copy_thread(void *data)
@@ -453,6 +457,7 @@ static int _copy_thread(void *data)
 	struct copy_brick *brick = data;
 
 	MARS_DBG("--------------- copy_thread %p starting\n", brick);
+	brick->copy_error = 0;
 	mars_power_led_on((void*)brick, true);
 	brick->trigger = true;
 
@@ -460,18 +465,25 @@ static int _copy_thread(void *data)
 		loff_t old_start = brick->copy_start;
 		loff_t old_end = brick->copy_end;
 		if (old_end > 0) {
-			_run_copy(brick);
+			int status = _run_copy(brick);
+			if (unlikely(status < 0)) {
+				brick->copy_error = status;
+				if (brick->abort_mode) {
+					MARS_INF("IO error, terminating prematurely, status = %d\n", status);
+					break;
+				}
+			}
 			msleep(10); // yield FIXME: remove this, use event handling for over/underflow
 		}
 
 		wait_event_interruptible_timeout(brick->event,
 						 brick->trigger || brick->copy_start != old_start || brick->copy_end != old_end || kthread_should_stop(),
 
-						 5 * HZ);
+						 1 * HZ);
 		brick->trigger = false;
 	}
 
-	MARS_DBG("--------------- copy_thread terminating\n");
+	MARS_DBG("--------------- copy_thread terminating (%d requests flying)\n", atomic_read(&brick->copy_flight));
 	wait_event_interruptible_timeout(brick->event, !atomic_read(&brick->copy_flight), 300 * HZ);
 	mars_power_led_off((void*)brick, true);
 	MARS_DBG("--------------- copy_thread done.\n");
@@ -545,7 +557,7 @@ static int copy_switch(struct copy_brick *brick)
 		mars_power_led_on((void*)brick, false);
 		if (brick->thread) {
 			MARS_INF("stopping thread...\n");
-			kthread_stop_nowait(brick->thread);
+			kthread_stop(brick->thread);
 			put_task_struct(brick->thread);
 			brick->thread = NULL;
 			wake_up_interruptible(&brick->event);
diff --git a/mars_copy.h b/mars_copy.h
index f66e7d09..c5e45fad 100644
--- a/mars_copy.h
+++ b/mars_copy.h
@@ -48,8 +48,10 @@ struct copy_brick {
 	int append_mode; // 1 = passively, 2 = actively
 	bool verify_mode;
 	bool utilize_mode; // utilize already copied data
+	bool abort_mode; // abort on IO error (default is retry forever)
 	// readonly from outside
 	loff_t copy_last; // current working position
+	int copy_error;
 	bool low_dirty;
 	// internal
 	volatile bool trigger;