diff --git a/weed/stats/metrics.go b/weed/stats/metrics.go
index 49a3b090b..f61f68e08 100644
--- a/weed/stats/metrics.go
+++ b/weed/stats/metrics.go
@@ -70,6 +70,14 @@ var (
 			Help:      "replica placement mismatch",
 		}, []string{"collection", "id"})
 
+	MasterVolumeLayout = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: Namespace,
+			Subsystem: "master",
+			Name:      "volume_layout_total",
+			Help:      "Number of volumes in volume layouts",
+		}, []string{"collection", "replica", "type"})
+
 	MasterLeaderChangeCounter = prometheus.NewCounterVec(
 		prometheus.CounterOpts{
 			Namespace: Namespace,
@@ -259,6 +267,7 @@ func init() {
 	Gather.MustRegister(MasterReceivedHeartbeatCounter)
 	Gather.MustRegister(MasterLeaderChangeCounter)
 	Gather.MustRegister(MasterReplicaPlacementMismatch)
+	Gather.MustRegister(MasterVolumeLayout)
 
 	Gather.MustRegister(FilerRequestCounter)
 	Gather.MustRegister(FilerHandlerCounter)
diff --git a/weed/topology/volume_growth_test.go b/weed/topology/volume_growth_test.go
index c3ba65d39..a3473c677 100644
--- a/weed/topology/volume_growth_test.go
+++ b/weed/topology/volume_growth_test.go
@@ -3,6 +3,7 @@ package topology
 import (
 	"encoding/json"
 	"fmt"
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
 	"testing"
 
 	"github.com/seaweedfs/seaweedfs/weed/sequence"
@@ -88,19 +89,35 @@ func setup(topologyLayout string) *Topology {
 		dcMap := dcValue.(map[string]interface{})
 		topo.LinkChildNode(dc)
 		for rackKey, rackValue := range dcMap {
-			rack := NewRack(rackKey)
+			dcRack := NewRack(rackKey)
 			rackMap := rackValue.(map[string]interface{})
-			dc.LinkChildNode(rack)
+			dc.LinkChildNode(dcRack)
 			for serverKey, serverValue := range rackMap {
 				server := NewDataNode(serverKey)
 				serverMap := serverValue.(map[string]interface{})
-				rack.LinkChildNode(server)
+				if ip, ok := serverMap["ip"]; ok {
+					server.Ip = ip.(string)
+				}
+				dcRack.LinkChildNode(server)
 				for _, v := range serverMap["volumes"].([]interface{}) {
 					m := v.(map[string]interface{})
 					vi := storage.VolumeInfo{
 						Id:      needle.VolumeId(int64(m["id"].(float64))),
 						Size:    uint64(m["size"].(float64)),
-						Version: needle.CurrentVersion}
+						Version: needle.CurrentVersion,
+					}
+					if mVal, ok := m["collection"]; ok {
+						vi.Collection = mVal.(string)
+					}
+					if mVal, ok := m["replication"]; ok {
+						rp, _ := super_block.NewReplicaPlacementFromString(mVal.(string))
+						vi.ReplicaPlacement = rp
+					}
+					if vi.ReplicaPlacement != nil {
+						vl := topo.GetVolumeLayout(vi.Collection, vi.ReplicaPlacement, needle.EMPTY_TTL, types.HardDriveType)
+						vl.RegisterVolume(&vi, server)
+						vl.setVolumeWritable(vi.Id)
+					}
 					server.AddOrUpdateVolume(vi)
 				}
 
@@ -346,3 +363,88 @@ func TestFindEmptySlotsForOneVolumeScheduleByWeight(t *testing.T) {
 		fmt.Printf("%s : %d\n", k, v)
 	}
 }
+
+var topologyLayout4 = `
+{
+  "dc1":{
+    "rack1":{
+      "serverdc111":{
+		"ip": "127.0.0.1",
+        "volumes":[
+          {"id":1, "size":12312, "collection":"test", "replication":"001"},
+          {"id":2, "size":12312, "collection":"test", "replication":"100"},
+          {"id":4, "size":12312, "collection":"test", "replication":"100"},
+          {"id":6, "size":12312, "collection":"test", "replication":"010"}
+        ],
+        "limit":100
+      }
+    }
+  },
+  "dc2":{
+    "rack1":{
+      "serverdc211":{
+		"ip": "127.0.0.2",
+        "volumes":[
+          {"id":2, "size":12312, "collection":"test", "replication":"100"},
+          {"id":3, "size":12312, "collection":"test", "replication":"010"},
+          {"id":5, "size":12312, "collection":"test", "replication":"001"},
+          {"id":6, "size":12312, "collection":"test", "replication":"010"}
+		],
+        "limit":100
+      }
+    }
+  },
+  "dc3":{
+    "rack1":{
+      "serverdc311":{
+		"ip": "127.0.0.3",
+        "volumes":[
+          {"id":1, "size":12312, "collection":"test", "replication":"001"},
+          {"id":3, "size":12312, "collection":"test", "replication":"010"},
+          {"id":4, "size":12312, "collection":"test", "replication":"100"},
+          {"id":5, "size":12312, "collection":"test", "replication":"001"}
+		],
+        "limit":100
+      }
+    }
+  }
+}
+`
+
+func TestPickForWrite(t *testing.T) {
+	topo := setup(topologyLayout4)
+	volumeGrowOption := &VolumeGrowOption{
+		Collection: "test",
+		DataCenter: "",
+		Rack:       "",
+		DataNode:   "",
+	}
+	for _, rpStr := range []string{"001", "010", "100"} {
+		rp, _ := super_block.NewReplicaPlacementFromString(rpStr)
+		vl := topo.GetVolumeLayout("test", rp, needle.EMPTY_TTL, types.HardDriveType)
+		volumeGrowOption.ReplicaPlacement = rp
+		for _, dc := range []string{"", "dc1", "dc2", "dc3"} {
+			volumeGrowOption.DataCenter = dc
+			for _, r := range []string{""} {
+				volumeGrowOption.Rack = r
+				for _, dn := range []string{""} {
+					if dc == "" && dn != "" {
+						continue
+					}
+					volumeGrowOption.DataNode = dn
+					fileId, count, _, _, err := topo.PickForWrite(1, volumeGrowOption, vl)
+					if err != nil {
+						fmt.Println(dc, r, dn, "pick for write error :", err)
+						t.Fail()
+					} else if count == 0 {
+						fmt.Println(dc, r, dn, "pick for write count is zero")
+						t.Fail()
+					} else if len(fileId) == 0 {
+						fmt.Println(dc, r, dn, "pick for write file id is empty")
+						t.Fail()
+					}
+				}
+			}
+		}
+	}
+}
diff --git a/weed/topology/volume_layout.go b/weed/topology/volume_layout.go
index 6b5d0b8da..278978292 100644
--- a/weed/topology/volume_layout.go
+++ b/weed/topology/volume_layout.go
@@ -3,6 +3,7 @@ package topology
 import (
 	"errors"
 	"fmt"
+	"github.com/seaweedfs/seaweedfs/weed/stats"
 	"math/rand"
 	"sync"
 	"sync/atomic"
@@ -349,18 +350,21 @@ func (vl *VolumeLayout) DoneGrowRequest() {
 }
 
 func (vl *VolumeLayout) ShouldGrowVolumes(option *VolumeGrowOption) bool {
-	active, crowded := vl.GetActiveVolumeCount(option)
+	total, active, crowded := vl.GetActiveVolumeCount(option)
+	stats.MasterVolumeLayout.WithLabelValues(option.Collection, option.ReplicaPlacement.String(), "total").Set(float64(total))
+	stats.MasterVolumeLayout.WithLabelValues(option.Collection, option.ReplicaPlacement.String(), "active").Set(float64(active))
+	stats.MasterVolumeLayout.WithLabelValues(option.Collection, option.ReplicaPlacement.String(), "crowded").Set(float64(crowded))
 	//glog.V(0).Infof("active volume: %d, high usage volume: %d\n", active, high)
 	return active <= crowded
 }
 
-func (vl *VolumeLayout) GetActiveVolumeCount(option *VolumeGrowOption) (active, crowded int) {
+func (vl *VolumeLayout) GetActiveVolumeCount(option *VolumeGrowOption) (total, active, crowded int) {
 	vl.accessLock.RLock()
 	defer vl.accessLock.RUnlock()
-
 	if option.DataCenter == "" {
-		return len(vl.writables), len(vl.crowded)
+		return len(vl.writables), len(vl.writables), len(vl.crowded)
 	}
+	total = len(vl.writables)
 	for _, v := range vl.writables {
 		for _, dn := range vl.vid2location[v].list {
 			if dn.GetDataCenter().Id() == NodeId(option.DataCenter) {