diff --git a/go/storage/needle.go b/go/storage/needle.go
index 5b4357614..11610dd80 100644
--- a/go/storage/needle.go
+++ b/go/storage/needle.go
@@ -25,6 +25,7 @@ const (
 )
 
 /*
+* A Needle means a uploaded and stored file.
 * Needle file size is limited to 4GB for now.
  */
 type Needle struct {
diff --git a/go/storage/store.go b/go/storage/store.go
index 80d8a30b8..e1d9d2b01 100644
--- a/go/storage/store.go
+++ b/go/storage/store.go
@@ -33,6 +33,10 @@ type MasterNodes struct {
 	lastNode int
 }
 
+func (mn *MasterNodes) String() string {
+	return fmt.Sprintf("nodes:%v, lastNode:%d", mn.nodes, mn.lastNode)
+}
+
 func NewMasterNodes(bootstrapNode string) (mn *MasterNodes) {
 	mn = &MasterNodes{nodes: []string{bootstrapNode}, lastNode: -1}
 	return
@@ -65,6 +69,9 @@ func (mn *MasterNodes) findMaster() (string, error) {
 	return mn.nodes[mn.lastNode], nil
 }
 
+/*
+ * A VolumeServer contains one Store
+ */
 type Store struct {
 	Port            int
 	Ip              string
@@ -77,6 +84,11 @@ type Store struct {
 	masterNodes     *MasterNodes
 }
 
+func (s *Store) String() (str string) {
+	str = fmt.Sprintf("Ip:%s, Port:%d, PublicUrl:%s, dataCenter:%s, rack:%s, connected:%v, volumeSizeLimit:%d, masterNodes:%s", s.Ip, s.Port, s.PublicUrl, s.dataCenter, s.rack, s.connected, s.volumeSizeLimit, s.masterNodes)
+	return
+}
+
 func NewStore(port int, ip, publicUrl string, dirnames []string, maxVolumeCounts []int) (s *Store) {
 	s = &Store{Port: port, Ip: ip, PublicUrl: publicUrl}
 	s.Locations = make([]*DiskLocation, 0)
diff --git a/go/storage/volume.go b/go/storage/volume.go
index 5b0a83605..a1eccd62c 100644
--- a/go/storage/volume.go
+++ b/go/storage/volume.go
@@ -33,6 +33,10 @@ func NewVolume(dirname string, collection string, id VolumeId, replicaPlacement
 	e = v.load(true, true)
 	return
 }
+func (v *Volume) String() string {
+	return fmt.Sprintf("Id:%v, dir:%s, Collection:%s, dataFile:%v, nm:%v, readOnly:%v", v.Id, v.dir, v.Collection, v.dataFile, v.nm, v.readOnly)
+}
+
 func loadVolumeWithoutIndex(dirname string, collection string, id VolumeId) (v *Volume, e error) {
 	v = &Volume{dir: dirname, Collection: collection, Id: id}
 	v.SuperBlock = SuperBlock{}
@@ -135,7 +139,7 @@ func (v *Volume) isFileUnchanged(n *Needle) bool {
 		oldNeedle := new(Needle)
 		oldNeedle.Read(v.dataFile, int64(nv.Offset)*NeedlePaddingSize, nv.Size, v.Version())
 		if oldNeedle.Checksum == n.Checksum && bytes.Equal(oldNeedle.Data, n.Data) {
-			n.Size = oldNeedle.Size
+			n.DataSize = oldNeedle.DataSize
 			return true
 		}
 	}
@@ -165,7 +169,7 @@ func (v *Volume) write(n *Needle) (size uint32, err error) {
 	v.accessLock.Lock()
 	defer v.accessLock.Unlock()
 	if v.isFileUnchanged(n) {
-		size = n.Size
+		size = n.DataSize
 		glog.V(4).Infof("needle is unchanged!")
 		return
 	}