diff --git a/go/topology/volume_layout.go b/go/topology/volume_layout.go
index 7d7e3f662..9664d3748 100644
--- a/go/topology/volume_layout.go
+++ b/go/topology/volume_layout.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"log"
 	"math/rand"
+	"sync"
 )
 
 type VolumeLayout struct {
@@ -13,6 +14,7 @@ type VolumeLayout struct {
 	writables       []storage.VolumeId // transient array of writable volume id
 	pulse           int64
 	volumeSizeLimit uint64
+	accessLock      sync.Mutex
 }
 
 func NewVolumeLayout(repType storage.ReplicationType, volumeSizeLimit uint64, pulse int64) *VolumeLayout {
@@ -26,6 +28,9 @@ func NewVolumeLayout(repType storage.ReplicationType, volumeSizeLimit uint64, pu
 }
 
 func (vl *VolumeLayout) RegisterVolume(v *storage.VolumeInfo, dn *DataNode) {
+	vl.accessLock.Lock()
+	defer vl.accessLock.Unlock()
+
 	if _, ok := vl.vid2location[v.Id]; !ok {
 		vl.vid2location[v.Id] = NewVolumeLocationList()
 	}
@@ -121,6 +126,9 @@ func (vl *VolumeLayout) setVolumeWritable(vid storage.VolumeId) bool {
 }
 
 func (vl *VolumeLayout) SetVolumeUnavailable(dn *DataNode, vid storage.VolumeId) bool {
+	vl.accessLock.Lock()
+	defer vl.accessLock.Unlock()
+
 	if vl.vid2location[vid].Remove(dn) {
 		if vl.vid2location[vid].Length() < vl.repType.GetCopyCount() {
 			log.Println("Volume", vid, "has", vl.vid2location[vid].Length(), "replica, less than required", vl.repType.GetCopyCount())
@@ -130,6 +138,9 @@ func (vl *VolumeLayout) SetVolumeUnavailable(dn *DataNode, vid storage.VolumeId)
 	return false
 }
 func (vl *VolumeLayout) SetVolumeAvailable(dn *DataNode, vid storage.VolumeId) bool {
+	vl.accessLock.Lock()
+	defer vl.accessLock.Unlock()
+
 	if vl.vid2location[vid].Add(dn) {
 		if vl.vid2location[vid].Length() >= vl.repType.GetCopyCount() {
 			return vl.setVolumeWritable(vid)
@@ -139,6 +150,10 @@ func (vl *VolumeLayout) SetVolumeAvailable(dn *DataNode, vid storage.VolumeId) b
 }
 
 func (vl *VolumeLayout) SetVolumeCapacityFull(vid storage.VolumeId) bool {
+	vl.accessLock.Lock()
+	defer vl.accessLock.Unlock()
+
+	log.Println("Volume", vid, "reaches full capacity.")
 	return vl.removeFromWritable(vid)
 }