diff --git a/go/topology/data_node.go b/go/topology/data_node.go
index fe0926e85..01419a791 100644
--- a/go/topology/data_node.go
+++ b/go/topology/data_node.go
@@ -3,6 +3,7 @@ package topology
 import (
 	"fmt"
 	"strconv"
+	"sync"
 
 	"github.com/chrislusf/seaweedfs/go/glog"
 	"github.com/chrislusf/seaweedfs/go/storage"
@@ -10,6 +11,7 @@ import (
 
 type DataNode struct {
 	NodeImpl
+	sync.RWMutex
 	volumes   map[storage.VolumeId]storage.VolumeInfo
 	Ip        string
 	Port      int
@@ -28,10 +30,14 @@ func NewDataNode(id string) *DataNode {
 }
 
 func (dn *DataNode) String() string {
+	dn.RLock()
+	defer dn.RUnlock()
 	return fmt.Sprintf("Node:%s, volumes:%v, Ip:%s, Port:%d, PublicUrl:%s, Dead:%v", dn.NodeImpl.String(), dn.volumes, dn.Ip, dn.Port, dn.PublicUrl, dn.Dead)
 }
 
 func (dn *DataNode) AddOrUpdateVolume(v storage.VolumeInfo) {
+	dn.Lock()
+	defer dn.Unlock()
 	if _, ok := dn.volumes[v.Id]; !ok {
 		dn.volumes[v.Id] = v
 		dn.UpAdjustVolumeCountDelta(1)
@@ -49,6 +55,7 @@ func (dn *DataNode) UpdateVolumes(actualVolumes []storage.VolumeInfo) (deletedVo
 	for _, v := range actualVolumes {
 		actualVolumeMap[v.Id] = v
 	}
+	dn.RLock()
 	for vid, v := range dn.volumes {
 		if _, ok := actualVolumeMap[vid]; !ok {
 			glog.V(0).Infoln("Deleting volume id:", vid)
@@ -58,12 +65,22 @@ func (dn *DataNode) UpdateVolumes(actualVolumes []storage.VolumeInfo) (deletedVo
 			dn.UpAdjustActiveVolumeCountDelta(-1)
 		}
 	} //TODO: adjust max volume id, if need to reclaim volume ids
+	dn.RUnlock()
 	for _, v := range actualVolumes {
 		dn.AddOrUpdateVolume(v)
 	}
 	return
 }
 
+func (dn *DataNode) GetVolumes() (ret []storage.VolumeInfo) {
+	dn.RLock()
+	for _, v := range dn.volumes {
+		ret = append(ret, v)
+	}
+	dn.RUnlock()
+	return ret
+}
+
 func (dn *DataNode) GetDataCenter() *DataCenter {
 	return dn.Parent().Parent().(*NodeImpl).value.(*DataCenter)
 }
diff --git a/go/topology/node.go b/go/topology/node.go
index f48f18236..356c0abeb 100644
--- a/go/topology/node.go
+++ b/go/topology/node.go
@@ -231,7 +231,7 @@ func (n *NodeImpl) CollectDeadNodeAndFullVolumes(freshThreshHold int64, volumeSi
 					n.GetTopology().chanDeadDataNodes <- dn
 				}
 			}
-			for _, v := range dn.volumes {
+			for _, v := range dn.GetVolumes() {
 				if uint64(v.Size) >= volumeSizeLimit {
 					//fmt.Println("volume",v.Id,"size",v.Size,">",volumeSizeLimit)
 					n.GetTopology().chanFullVolumes <- v
diff --git a/go/topology/topology_event_handling.go b/go/topology/topology_event_handling.go
index 3879fbaba..8a3cc5a89 100644
--- a/go/topology/topology_event_handling.go
+++ b/go/topology/topology_event_handling.go
@@ -54,7 +54,7 @@ func (t *Topology) SetVolumeCapacityFull(volumeInfo storage.VolumeInfo) bool {
 	return true
 }
 func (t *Topology) UnRegisterDataNode(dn *DataNode) {
-	for _, v := range dn.volumes {
+	for _, v := range dn.GetVolumes() {
 		glog.V(0).Infoln("Removing Volume", v.Id, "from the dead volume server", dn)
 		vl := t.GetVolumeLayout(v.Collection, v.ReplicaPlacement, v.Ttl)
 		vl.SetVolumeUnavailable(dn, v.Id)
@@ -65,7 +65,7 @@ func (t *Topology) UnRegisterDataNode(dn *DataNode) {
 	dn.Parent().UnlinkChildNode(dn.Id())
 }
 func (t *Topology) RegisterRecoveredDataNode(dn *DataNode) {
-	for _, v := range dn.volumes {
+	for _, v := range dn.GetVolumes() {
 		vl := t.GetVolumeLayout(v.Collection, v.ReplicaPlacement, v.Ttl)
 		if vl.isWritable(&v) {
 			vl.SetVolumeAvailable(dn, v.Id)
diff --git a/go/topology/topology_map.go b/go/topology/topology_map.go
index 6a1423ca8..dff11aaad 100644
--- a/go/topology/topology_map.go
+++ b/go/topology/topology_map.go
@@ -39,7 +39,7 @@ func (t *Topology) ToVolumeMap() interface{} {
 			for _, d := range rack.Children() {
 				dn := d.(*DataNode)
 				var volumes []interface{}
-				for _, v := range dn.volumes {
+				for _, v := range dn.GetVolumes() {
 					volumes = append(volumes, v)
 				}
 				dataNodes[d.Id()] = volumes