diff --git a/go/operation/lookup.go b/go/operation/lookup.go
index e6b6658da..70bc7146e 100644
--- a/go/operation/lookup.go
+++ b/go/operation/lookup.go
@@ -3,7 +3,7 @@ package operation
 import (
 	"encoding/json"
 	"errors"
-	_ "fmt"
+	"fmt"
 	"math/rand"
 	"net/url"
 	"strings"
@@ -22,6 +22,10 @@ type LookupResult struct {
 	Error     string     `json:"error,omitempty"`
 }
 
+func (lr *LookupResult) String() string {
+	return fmt.Sprintf("VolumeId:%s, Locations:%v, Error:%s", lr.VolumeId, lr.Locations, lr.Error)
+}
+
 var (
 	vc VidCache
 )
diff --git a/go/storage/volume_info.go b/go/storage/volume_info.go
index 6410c1784..bc8049ea4 100644
--- a/go/storage/volume_info.go
+++ b/go/storage/volume_info.go
@@ -1,6 +1,7 @@
 package storage
 
 import (
+	"fmt"
 	"github.com/chrislusf/weed-fs/go/operation"
 )
 
@@ -36,3 +37,7 @@ func NewVolumeInfo(m *operation.VolumeInformationMessage) (vi VolumeInfo, err er
 	vi.Ttl = LoadTTLFromUint32(*m.Ttl)
 	return vi, nil
 }
+
+func (vi VolumeInfo) String() string {
+	return fmt.Sprintf("Id:%s, Size:%d, ReplicaPlacement:%s, Collection:%s, Version:%v, FileCount:%d, DeleteCount:%d, DeletedByteCount:%d, ReadOnly:%v", vi.Id, vi.Size, vi.ReplicaPlacement, vi.Collection, vi.Version, vi.FileCount, vi.DeleteCount, vi.DeletedByteCount, vi.ReadOnly)
+}
diff --git a/go/topology/collection.go b/go/topology/collection.go
index 4b47ae88a..5437ffd79 100644
--- a/go/topology/collection.go
+++ b/go/topology/collection.go
@@ -1,6 +1,8 @@
 package topology
 
 import (
+	"fmt"
+
 	"github.com/chrislusf/weed-fs/go/storage"
 	"github.com/chrislusf/weed-fs/go/util"
 )
@@ -17,6 +19,10 @@ func NewCollection(name string, volumeSizeLimit uint64) *Collection {
 	return c
 }
 
+func (c *Collection) String() string {
+	return fmt.Sprintf("Name:%s, volumeSizeLimit:%d, storageType2VolumeLayout:%v", c.Name, c.volumeSizeLimit, c.storageType2VolumeLayout)
+}
+
 func (c *Collection) GetOrCreateVolumeLayout(rp *storage.ReplicaPlacement, ttl *storage.TTL) *VolumeLayout {
 	keyString := rp.String()
 	if ttl != nil {
diff --git a/go/topology/data_node.go b/go/topology/data_node.go
index 109bd037f..09b9fac6c 100644
--- a/go/topology/data_node.go
+++ b/go/topology/data_node.go
@@ -1,6 +1,7 @@
 package topology
 
 import (
+	"fmt"
 	"strconv"
 
 	"github.com/chrislusf/weed-fs/go/glog"
@@ -26,6 +27,10 @@ func NewDataNode(id string) *DataNode {
 	return s
 }
 
+func (dn *DataNode) String() string {
+	return fmt.Sprintf("NodeImpl:%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) {
 	if _, ok := dn.volumes[v.Id]; !ok {
 		dn.volumes[v.Id] = v
diff --git a/go/topology/volume_growth.go b/go/topology/volume_growth.go
index b1f241990..6124c0da2 100644
--- a/go/topology/volume_growth.go
+++ b/go/topology/volume_growth.go
@@ -30,6 +30,10 @@ type VolumeGrowth struct {
 	accessLock sync.Mutex
 }
 
+func (o *VolumeGrowOption) String() string {
+	return fmt.Sprintf("Collection:%s, ReplicaPlacement:%v, Ttl:%v, DataCenter:%s, Rack:%s, DataNode:%s", o.Collection, o.ReplicaPlacement, o.Ttl, o.DataCenter, o.Rack, o.DataNode)
+}
+
 func NewDefaultVolumeGrowth() *VolumeGrowth {
 	return &VolumeGrowth{}
 }
diff --git a/go/topology/volume_layout.go b/go/topology/volume_layout.go
index de72bf895..4b1d3dad9 100644
--- a/go/topology/volume_layout.go
+++ b/go/topology/volume_layout.go
@@ -2,6 +2,7 @@ package topology
 
 import (
 	"errors"
+	"fmt"
 	"math/rand"
 	"sync"
 
@@ -29,6 +30,10 @@ func NewVolumeLayout(rp *storage.ReplicaPlacement, ttl *storage.TTL, volumeSizeL
 	}
 }
 
+func (vl *VolumeLayout) String() string {
+	return fmt.Sprintf("rp:%v, ttl:%v, vid2location:%v, writables:%v, volumeSizeLimit:%v", vl.rp, vl.ttl, vl.vid2location, vl.writables, vl.volumeSizeLimit)
+}
+
 func (vl *VolumeLayout) RegisterVolume(v *storage.VolumeInfo, dn *DataNode) {
 	vl.accessLock.Lock()
 	defer vl.accessLock.Unlock()
diff --git a/go/topology/volume_location_list.go b/go/topology/volume_location_list.go
index 011614013..0f892c010 100644
--- a/go/topology/volume_location_list.go
+++ b/go/topology/volume_location_list.go
@@ -1,5 +1,9 @@
 package topology
 
+import (
+	"fmt"
+)
+
 type VolumeLocationList struct {
 	list []*DataNode
 }
@@ -8,6 +12,10 @@ func NewVolumeLocationList() *VolumeLocationList {
 	return &VolumeLocationList{}
 }
 
+func (dnll *VolumeLocationList) String() string {
+	return fmt.Sprintf("%v", dnll.list)
+}
+
 func (dnll *VolumeLocationList) Head() *DataNode {
 	return dnll.list[0]
 }
diff --git a/go/util/concurrent_read_map.go b/go/util/concurrent_read_map.go
index d16fdbcaf..880fe54e3 100644
--- a/go/util/concurrent_read_map.go
+++ b/go/util/concurrent_read_map.go
@@ -1,6 +1,8 @@
 package util
 
-import "sync"
+import (
+	"sync"
+)
 
 // A mostly for read map, which can thread-safely
 // initialize the map entries.