diff --git a/weed/s3api/stats.go b/weed/s3api/stats.go
index cd04b9970..415ec55dd 100644
--- a/weed/s3api/stats.go
+++ b/weed/s3api/stats.go
@@ -11,6 +11,10 @@ import (
 
 func track(f http.HandlerFunc, action string) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
+		inFlightGauge := stats_collect.S3InFlightRequestsGauge.WithLabelValues(action)
+		inFlightGauge.Inc()
+		defer inFlightGauge.Dec()
+
 		bucket, _ := s3_constants.GetBucketAndObject(r)
 		w.Header().Set("Server", "SeaweedFS "+util.VERSION)
 		recorder := stats_collect.NewStatusResponseWriter(w)
diff --git a/weed/server/filer_server_handlers.go b/weed/server/filer_server_handlers.go
index 69774ce27..1c5c89dcf 100644
--- a/weed/server/filer_server_handlers.go
+++ b/weed/server/filer_server_handlers.go
@@ -21,6 +21,11 @@ import (
 
 func (fs *FilerServer) filerHandler(w http.ResponseWriter, r *http.Request) {
 	start := time.Now()
+
+	inFlightGauge := stats.FilerInFlightRequestsGauge.WithLabelValues(r.Method)
+	inFlightGauge.Inc()
+	defer inFlightGauge.Dec()
+
 	statusRecorder := stats.NewStatusResponseWriter(w)
 	w = statusRecorder
 	origin := r.Header.Get("Origin")
diff --git a/weed/server/volume_server_handlers.go b/weed/server/volume_server_handlers.go
index 85fb9ba81..22ef0e1c8 100644
--- a/weed/server/volume_server_handlers.go
+++ b/weed/server/volume_server_handlers.go
@@ -31,6 +31,10 @@ security settings:
 */
 
 func (vs *VolumeServer) privateStoreHandler(w http.ResponseWriter, r *http.Request) {
+	inFlightGauge := stats.VolumeServerInFlightRequestsGauge.WithLabelValues(r.Method)
+	inFlightGauge.Inc()
+	defer inFlightGauge.Dec()
+
 	statusRecorder := stats.NewStatusResponseWriter(w)
 	w = statusRecorder
 	w.Header().Set("Server", "SeaweedFS Volume "+util.VERSION)
diff --git a/weed/stats/metrics.go b/weed/stats/metrics.go
index 956bf4009..93f80c1f4 100644
--- a/weed/stats/metrics.go
+++ b/weed/stats/metrics.go
@@ -127,6 +127,14 @@ var (
 			Buckets:   prometheus.ExponentialBuckets(0.0001, 2, 24),
 		}, []string{"type"})
 
+	FilerInFlightRequestsGauge = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: Namespace,
+			Subsystem: "filer",
+			Name:      "in_flight_requests",
+			Help:      "Current number of in-flight requests being handled by filer.",
+		}, []string{"type"})
+
 	FilerServerLastSendTsOfSubscribeGauge = prometheus.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Namespace: Namespace,
@@ -210,6 +218,14 @@ var (
 			Buckets:   prometheus.ExponentialBuckets(0.0001, 2, 24),
 		}, []string{"type"})
 
+	VolumeServerInFlightRequestsGauge = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: Namespace,
+			Subsystem: "volumeServer",
+			Name:      "in_flight_requests",
+			Help:      "Current number of in-flight requests being handled by volume server.",
+		}, []string{"type"})
+
 	VolumeServerVolumeGauge = prometheus.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Namespace: Namespace,
@@ -280,6 +296,13 @@ var (
 			Help:      "Bucketed histogram of s3 time to first byte request processing time.",
 			Buckets:   prometheus.ExponentialBuckets(0.001, 2, 27),
 		}, []string{"type", "bucket"})
+	S3InFlightRequestsGauge = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: Namespace,
+			Subsystem: "s3",
+			Name:      "in_flight_requests",
+			Help:      "Current number of in-flight requests being handled by s3.",
+		}, []string{"type"})
 )
 
 func init() {
@@ -295,6 +318,7 @@ func init() {
 	Gather.MustRegister(FilerRequestCounter)
 	Gather.MustRegister(FilerHandlerCounter)
 	Gather.MustRegister(FilerRequestHistogram)
+	Gather.MustRegister(FilerInFlightRequestsGauge)
 	Gather.MustRegister(FilerStoreCounter)
 	Gather.MustRegister(FilerStoreHistogram)
 	Gather.MustRegister(FilerSyncOffsetGauge)
@@ -305,6 +329,7 @@ func init() {
 	Gather.MustRegister(VolumeServerRequestCounter)
 	Gather.MustRegister(VolumeServerHandlerCounter)
 	Gather.MustRegister(VolumeServerRequestHistogram)
+	Gather.MustRegister(VolumeServerInFlightRequestsGauge)
 	Gather.MustRegister(VolumeServerVacuumingCompactCounter)
 	Gather.MustRegister(VolumeServerVacuumingCommitCounter)
 	Gather.MustRegister(VolumeServerVacuumingHistogram)
@@ -317,6 +342,7 @@ func init() {
 	Gather.MustRegister(S3RequestCounter)
 	Gather.MustRegister(S3HandlerCounter)
 	Gather.MustRegister(S3RequestHistogram)
+	Gather.MustRegister(S3InFlightRequestsGauge)
 	Gather.MustRegister(S3TimeToFirstByteHistogram)
 }
 
diff --git a/weed/topology/store_replicate.go b/weed/topology/store_replicate.go
index b4a7d649c..a2be991fa 100644
--- a/weed/topology/store_replicate.go
+++ b/weed/topology/store_replicate.go
@@ -47,6 +47,11 @@ func ReplicatedWrite(masterFn operation.GetMasterFn, grpcDialOption grpc.DialOpt
 
 	if s.GetVolume(volumeId) != nil {
 		start := time.Now()
+
+		inFlightGauge := stats.VolumeServerInFlightRequestsGauge.WithLabelValues(stats.WriteToLocalDisk)
+		inFlightGauge.Inc()
+		defer inFlightGauge.Dec()
+
 		isUnchanged, err = s.WriteVolumeNeedle(volumeId, n, true, fsync)
 		stats.VolumeServerRequestHistogram.WithLabelValues(stats.WriteToLocalDisk).Observe(time.Since(start).Seconds())
 		if err != nil {
@@ -59,6 +64,11 @@ func ReplicatedWrite(masterFn operation.GetMasterFn, grpcDialOption grpc.DialOpt
 
 	if len(remoteLocations) > 0 { //send to other replica locations
 		start := time.Now()
+
+		inFlightGauge := stats.VolumeServerInFlightRequestsGauge.WithLabelValues(stats.WriteToReplicas)
+		inFlightGauge.Inc()
+		defer inFlightGauge.Dec()
+
 		err = DistributedOperation(remoteLocations, func(location operation.Location) error {
 			u := url.URL{
 				Scheme: "http",