diff --git a/README.md b/README.md
index 6098a95a4..403ee7604 100644
--- a/README.md
+++ b/README.md
@@ -1175,6 +1175,7 @@ VictoriaMetrics also exposes currently running queries with their execution time
   has at least 20% of free space comparing to disk size. The remaining amount of free space
   can be [monitored](#monitoring) via `vm_free_disk_space_bytes` metric. The total size of data
   stored on the disk can be monitored via sum of `vm_data_size_bytes` metrics.
+  See also `vm_merge_need_free_disk_space` metrics, which are set to 1 if background merge cannot be initiated due to free disk space shortage.
 
 * If VictoriaMetrics doesn't work because of certain parts are corrupted due to disk errors,
   then just remove directories with broken parts. This will recover VictoriaMetrics at the cost
diff --git a/app/vmstorage/main.go b/app/vmstorage/main.go
index 8244c8a61..d9a6e69ed 100644
--- a/app/vmstorage/main.go
+++ b/app/vmstorage/main.go
@@ -399,10 +399,10 @@ func registerStorageMetrics() {
 	})
 
 	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/686
-	metrics.NewGauge(`vm_small_merge_need_free_disk_space`, func() float64 {
+	metrics.NewGauge(`vm_merge_need_free_disk_space{type="storage/small"}`, func() float64 {
 		return float64(tm().SmallMergeNeedFreeDiskSpace)
 	})
-	metrics.NewGauge(`vm_big_merge_need_free_disk_space`, func() float64 {
+	metrics.NewGauge(`vm_merge_need_free_disk_space{type="storage/big"}`, func() float64 {
 		return float64(tm().BigMergeNeedFreeDiskSpace)
 	})
 
diff --git a/docs/Single-server-VictoriaMetrics.md b/docs/Single-server-VictoriaMetrics.md
index 6098a95a4..403ee7604 100644
--- a/docs/Single-server-VictoriaMetrics.md
+++ b/docs/Single-server-VictoriaMetrics.md
@@ -1175,6 +1175,7 @@ VictoriaMetrics also exposes currently running queries with their execution time
   has at least 20% of free space comparing to disk size. The remaining amount of free space
   can be [monitored](#monitoring) via `vm_free_disk_space_bytes` metric. The total size of data
   stored on the disk can be monitored via sum of `vm_data_size_bytes` metrics.
+  See also `vm_merge_need_free_disk_space` metrics, which are set to 1 if background merge cannot be initiated due to free disk space shortage.
 
 * If VictoriaMetrics doesn't work because of certain parts are corrupted due to disk errors,
   then just remove directories with broken parts. This will recover VictoriaMetrics at the cost