diff --git a/weed/command/export.go b/weed/command/export.go
index 5a7dc71d9..0f7496472 100644
--- a/weed/command/export.go
+++ b/weed/command/export.go
@@ -118,7 +118,7 @@ func runExport(cmd *Command, args []string) bool {
 	}
 	defer indexFile.Close()
 
-	needleMap, err := storage.LoadNeedleMap(indexFile)
+	needleMap, err := storage.LoadBtreeNeedleMap(indexFile)
 	if err != nil {
 		glog.Fatalf("cannot load needle map from %s: %s", indexFile.Name(), err)
 	}
diff --git a/weed/command/fix.go b/weed/command/fix.go
index 22480dcd0..f3103c6c2 100644
--- a/weed/command/fix.go
+++ b/weed/command/fix.go
@@ -43,7 +43,7 @@ func runFix(cmd *Command, args []string) bool {
 	}
 	defer indexFile.Close()
 
-	nm := storage.NewNeedleMap(indexFile)
+	nm := storage.NewBtreeNeedleMap(indexFile)
 	defer nm.Close()
 
 	vid := storage.VolumeId(*fixVolumeId)
diff --git a/weed/command/server.go b/weed/command/server.go
index e1152f23f..ad6916b8f 100644
--- a/weed/command/server.go
+++ b/weed/command/server.go
@@ -72,7 +72,7 @@ var (
 	volumeDataFolders             = cmdServer.Flag.String("dir", os.TempDir(), "directories to store data files. dir[,dir]...")
 	volumeMaxDataVolumeCounts     = cmdServer.Flag.String("volume.max", "7", "maximum numbers of volumes, count[,count]...")
 	volumePulse                   = cmdServer.Flag.Int("pulseSeconds", 5, "number of seconds between heartbeats")
-	volumeIndexType               = cmdServer.Flag.String("volume.index", "memory", "Choose [memory|leveldb|boltdb] mode for memory~performance balance.")
+	volumeIndexType               = cmdServer.Flag.String("volume.index", "memory", "Choose [memory|leveldb|boltdb|btree] mode for memory~performance balance.")
 	volumeFixJpgOrientation       = cmdServer.Flag.Bool("volume.images.fix.orientation", true, "Adjust jpg orientation when uploading.")
 	volumeReadRedirect            = cmdServer.Flag.Bool("volume.read.redirect", true, "Redirect moved or non-local volumes.")
 	volumeServerPublicUrl         = cmdServer.Flag.String("volume.publicUrl", "", "publicly accessible address")
@@ -276,6 +276,8 @@ func runServer(cmd *Command, args []string) bool {
 		volumeNeedleMapKind = storage.NeedleMapLevelDb
 	case "boltdb":
 		volumeNeedleMapKind = storage.NeedleMapBoltDb
+	case "btree":
+		volumeNeedleMapKind = storage.NeedleMapBtree
 	}
 	volumeServer := weed_server.NewVolumeServer(volumeMux, publicVolumeMux,
 		*serverIp, *volumePort, *volumeServerPublicUrl,
diff --git a/weed/command/volume.go b/weed/command/volume.go
index 0e69325b6..a4e316ecb 100644
--- a/weed/command/volume.go
+++ b/weed/command/volume.go
@@ -52,7 +52,7 @@ func init() {
 	v.maxCpu = cmdVolume.Flag.Int("maxCpu", 0, "maximum number of CPUs. 0 means all available CPUs")
 	v.dataCenter = cmdVolume.Flag.String("dataCenter", "", "current volume server's data center name")
 	v.rack = cmdVolume.Flag.String("rack", "", "current volume server's rack name")
-	v.indexType = cmdVolume.Flag.String("index", "memory", "Choose [memory|leveldb|boltdb] mode for memory~performance balance.")
+	v.indexType = cmdVolume.Flag.String("index", "memory", "Choose [memory|leveldb|boltdb|btree] mode for memory~performance balance.")
 	v.fixJpgOrientation = cmdVolume.Flag.Bool("images.fix.orientation", true, "Adjust jpg orientation when uploading.")
 	v.readRedirect = cmdVolume.Flag.Bool("read.redirect", true, "Redirect moved or non-local volumes.")
 	v.enableBytesCache = cmdVolume.Flag.Bool("cache.enable", false, "direct cache instead of OS cache, cost more memory.")
@@ -126,6 +126,8 @@ func runVolume(cmd *Command, args []string) bool {
 		volumeNeedleMapKind = storage.NeedleMapLevelDb
 	case "boltdb":
 		volumeNeedleMapKind = storage.NeedleMapBoltDb
+	case "btree":
+		volumeNeedleMapKind = storage.NeedleMapBtree
 	}
 	volumeServer := weed_server.NewVolumeServer(volumeMux, publicVolumeMux,
 		*v.ip, *v.port, *v.publicUrl,
diff --git a/weed/storage/needle/btree_map.go b/weed/storage/needle/btree_map.go
new file mode 100644
index 000000000..64c0bacc1
--- /dev/null
+++ b/weed/storage/needle/btree_map.go
@@ -0,0 +1,52 @@
+package needle
+
+import (
+	"github.com/google/btree"
+)
+
+//This map assumes mostly inserting increasing keys
+type BtreeMap struct {
+	tree *btree.BTree
+}
+
+func NewBtreeMap() *BtreeMap {
+	return &BtreeMap{
+		tree: btree.New(32),
+	}
+}
+
+func (cm *BtreeMap) Set(key Key, offset, size uint32) (oldOffset, oldSize uint32) {
+	found := cm.tree.ReplaceOrInsert(NeedleValue{key, offset, size})
+	if found != nil {
+		old := found.(NeedleValue)
+		return old.Offset, old.Size
+	}
+	return
+}
+
+func (cm *BtreeMap) Delete(key Key) (oldSize uint32) {
+	found := cm.tree.Delete(NeedleValue{key, 0, 0})
+	if found != nil {
+		old := found.(NeedleValue)
+		return old.Size
+	}
+	return
+}
+func (cm *BtreeMap) Get(key Key) (*NeedleValue, bool) {
+	found := cm.tree.Get(NeedleValue{key, 0, 0})
+	if found != nil {
+		old := found.(NeedleValue)
+		return &old, true
+	}
+	return nil, false
+}
+
+// Visit visits all entries or stop if any error when visiting
+func (cm *BtreeMap) Visit(visit func(NeedleValue) error) (ret error) {
+	cm.tree.Ascend(func(item btree.Item) bool {
+		needle := item.(NeedleValue)
+		ret = visit(needle)
+		return ret == nil
+	})
+	return ret
+}
diff --git a/weed/storage/needle/compact_map.go b/weed/storage/needle/compact_map.go
new file mode 100644
index 000000000..ea2360fa7
--- /dev/null
+++ b/weed/storage/needle/compact_map.go
@@ -0,0 +1,194 @@
+package needle
+
+import (
+	"sync"
+)
+
+type CompactSection struct {
+	sync.RWMutex
+	values   []NeedleValue
+	overflow map[Key]NeedleValue
+	start    Key
+	end      Key
+	counter  int
+}
+
+func NewCompactSection(start Key) *CompactSection {
+	return &CompactSection{
+		values:   make([]NeedleValue, batch),
+		overflow: make(map[Key]NeedleValue),
+		start:    start,
+	}
+}
+
+//return old entry size
+func (cs *CompactSection) Set(key Key, offset, size uint32) (oldOffset, oldSize uint32) {
+	cs.Lock()
+	if key > cs.end {
+		cs.end = key
+	}
+	if i := cs.binarySearchValues(key); i >= 0 {
+		oldOffset, oldSize = cs.values[i].Offset, cs.values[i].Size
+		//println("key", key, "old size", ret)
+		cs.values[i].Offset, cs.values[i].Size = offset, size
+	} else {
+		needOverflow := cs.counter >= batch
+		needOverflow = needOverflow || cs.counter > 0 && cs.values[cs.counter-1].Key > key
+		if needOverflow {
+			//println("start", cs.start, "counter", cs.counter, "key", key)
+			if oldValue, found := cs.overflow[key]; found {
+				oldOffset, oldSize = oldValue.Offset, oldValue.Size
+			}
+			cs.overflow[key] = NeedleValue{Key: key, Offset: offset, Size: size}
+		} else {
+			p := &cs.values[cs.counter]
+			p.Key, p.Offset, p.Size = key, offset, size
+			//println("added index", cs.counter, "key", key, cs.values[cs.counter].Key)
+			cs.counter++
+		}
+	}
+	cs.Unlock()
+	return
+}
+
+//return old entry size
+func (cs *CompactSection) Delete(key Key) uint32 {
+	cs.Lock()
+	ret := uint32(0)
+	if i := cs.binarySearchValues(key); i >= 0 {
+		if cs.values[i].Size > 0 {
+			ret = cs.values[i].Size
+			cs.values[i].Size = 0
+		}
+	}
+	if v, found := cs.overflow[key]; found {
+		delete(cs.overflow, key)
+		ret = v.Size
+	}
+	cs.Unlock()
+	return ret
+}
+func (cs *CompactSection) Get(key Key) (*NeedleValue, bool) {
+	cs.RLock()
+	if v, ok := cs.overflow[key]; ok {
+		cs.RUnlock()
+		return &v, true
+	}
+	if i := cs.binarySearchValues(key); i >= 0 {
+		cs.RUnlock()
+		return &cs.values[i], true
+	}
+	cs.RUnlock()
+	return nil, false
+}
+func (cs *CompactSection) binarySearchValues(key Key) int {
+	l, h := 0, cs.counter-1
+	if h >= 0 && cs.values[h].Key < key {
+		return -2
+	}
+	//println("looking for key", key)
+	for l <= h {
+		m := (l + h) / 2
+		//println("mid", m, "key", cs.values[m].Key, cs.values[m].Offset, cs.values[m].Size)
+		if cs.values[m].Key < key {
+			l = m + 1
+		} else if key < cs.values[m].Key {
+			h = m - 1
+		} else {
+			//println("found", m)
+			return m
+		}
+	}
+	return -1
+}
+
+//This map assumes mostly inserting increasing keys
+//This map assumes mostly inserting increasing keys
+type CompactMap struct {
+	list []*CompactSection
+}
+
+func NewCompactMap() *CompactMap {
+	return &CompactMap{}
+}
+
+func (cm *CompactMap) Set(key Key, offset, size uint32) (oldOffset, oldSize uint32) {
+	x := cm.binarySearchCompactSection(key)
+	if x < 0 {
+		//println(x, "creating", len(cm.list), "section, starting", key)
+		cm.list = append(cm.list, NewCompactSection(key))
+		x = len(cm.list) - 1
+		//keep compact section sorted by start
+		for x > 0 {
+			if cm.list[x-1].start > cm.list[x].start {
+				cm.list[x-1], cm.list[x] = cm.list[x], cm.list[x-1]
+				x = x - 1
+			} else {
+				break
+			}
+		}
+	}
+	return cm.list[x].Set(key, offset, size)
+}
+func (cm *CompactMap) Delete(key Key) uint32 {
+	x := cm.binarySearchCompactSection(key)
+	if x < 0 {
+		return uint32(0)
+	}
+	return cm.list[x].Delete(key)
+}
+func (cm *CompactMap) Get(key Key) (*NeedleValue, bool) {
+	x := cm.binarySearchCompactSection(key)
+	if x < 0 {
+		return nil, false
+	}
+	return cm.list[x].Get(key)
+}
+func (cm *CompactMap) binarySearchCompactSection(key Key) int {
+	l, h := 0, len(cm.list)-1
+	if h < 0 {
+		return -5
+	}
+	if cm.list[h].start <= key {
+		if cm.list[h].counter < batch || key <= cm.list[h].end {
+			return h
+		}
+		return -4
+	}
+	for l <= h {
+		m := (l + h) / 2
+		if key < cm.list[m].start {
+			h = m - 1
+		} else { // cm.list[m].start <= key
+			if cm.list[m+1].start <= key {
+				l = m + 1
+			} else {
+				return m
+			}
+		}
+	}
+	return -3
+}
+
+// Visit visits all entries or stop if any error when visiting
+func (cm *CompactMap) Visit(visit func(NeedleValue) error) error {
+	for _, cs := range cm.list {
+		cs.RLock()
+		for _, v := range cs.overflow {
+			if err := visit(v); err != nil {
+				cs.RUnlock()
+				return err
+			}
+		}
+		for _, v := range cs.values {
+			if _, found := cs.overflow[v.Key]; !found {
+				if err := visit(v); err != nil {
+					cs.RUnlock()
+					return err
+				}
+			}
+		}
+		cs.RUnlock()
+	}
+	return nil
+}
diff --git a/weed/storage/compact_map_perf_test.go b/weed/storage/needle/compact_map_perf_test.go
similarity index 79%
rename from weed/storage/compact_map_perf_test.go
rename to weed/storage/needle/compact_map_perf_test.go
index cc7669139..8a26e7ed3 100644
--- a/weed/storage/compact_map_perf_test.go
+++ b/weed/storage/needle/compact_map_perf_test.go
@@ -1,4 +1,4 @@
-package storage
+package needle
 
 import (
 	"log"
@@ -11,15 +11,15 @@ import (
 
 func TestMemoryUsage(t *testing.T) {
 
-	indexFile, ie := os.OpenFile("../../test/sample.idx", os.O_RDWR|os.O_RDONLY, 0644)
+	indexFile, ie := os.OpenFile("../../../test/sample.idx", os.O_RDWR|os.O_RDONLY, 0644)
 	if ie != nil {
 		log.Fatalln(ie)
 	}
-	LoadNewNeedleMap(indexFile)
+	loadNewNeedleMap(indexFile)
 
 }
 
-func LoadNewNeedleMap(file *os.File) CompactMap {
+func loadNewNeedleMap(file *os.File) {
 	m := NewCompactMap()
 	bytes := make([]byte, 16*1024)
 	count, e := file.Read(bytes)
@@ -41,5 +41,4 @@ func LoadNewNeedleMap(file *os.File) CompactMap {
 
 		count, e = file.Read(bytes)
 	}
-	return m
 }
diff --git a/weed/storage/compact_map_test.go b/weed/storage/needle/compact_map_test.go
similarity index 99%
rename from weed/storage/compact_map_test.go
rename to weed/storage/needle/compact_map_test.go
index 1ccb48edb..4d574bafe 100644
--- a/weed/storage/compact_map_test.go
+++ b/weed/storage/needle/compact_map_test.go
@@ -1,4 +1,4 @@
-package storage
+package needle
 
 import (
 	"testing"
diff --git a/weed/storage/needle/needle_value.go b/weed/storage/needle/needle_value.go
new file mode 100644
index 000000000..137ab0814
--- /dev/null
+++ b/weed/storage/needle/needle_value.go
@@ -0,0 +1,28 @@
+package needle
+
+import (
+	"strconv"
+
+	"github.com/google/btree"
+)
+
+const (
+	batch = 100000
+)
+
+type NeedleValue struct {
+	Key    Key
+	Offset uint32 `comment:"Volume offset"` //since aligned to 8 bytes, range is 4G*8=32G
+	Size   uint32 `comment:"Size of the data portion"`
+}
+
+func (this NeedleValue) Less(than btree.Item) bool {
+	that := than.(NeedleValue)
+	return this.Key < that.Key
+}
+
+type Key uint64
+
+func (k Key) String() string {
+	return strconv.FormatUint(uint64(k), 10)
+}
diff --git a/weed/storage/needle/needle_value_map.go b/weed/storage/needle/needle_value_map.go
new file mode 100644
index 000000000..81f41b235
--- /dev/null
+++ b/weed/storage/needle/needle_value_map.go
@@ -0,0 +1,8 @@
+package needle
+
+type NeedleValueMap interface {
+	Set(key Key, offset, size uint32) (oldOffset, oldSize uint32)
+	Delete(key Key) uint32
+	Get(key Key) (*NeedleValue, bool)
+	Visit(visit func(NeedleValue) error) error
+}
diff --git a/weed/storage/needle_map.go b/weed/storage/needle_map.go
index 15a0387c5..14e4ccf3a 100644
--- a/weed/storage/needle_map.go
+++ b/weed/storage/needle_map.go
@@ -6,6 +6,7 @@ import (
 	"os"
 	"sync"
 
+	"github.com/chrislusf/seaweedfs/weed/storage/needle"
 	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
@@ -15,6 +16,7 @@ const (
 	NeedleMapInMemory NeedleMapType = iota
 	NeedleMapLevelDb
 	NeedleMapBoltDb
+	NeedleMapBtree
 )
 
 const (
@@ -23,7 +25,7 @@ const (
 
 type NeedleMapper interface {
 	Put(key uint64, offset uint32, size uint32) error
-	Get(key uint64) (element *NeedleValue, ok bool)
+	Get(key uint64) (element *needle.NeedleValue, ok bool)
 	Delete(key uint64, offset uint32) error
 	Close()
 	Destroy() error
diff --git a/weed/storage/needle_map_boltdb.go b/weed/storage/needle_map_boltdb.go
index e131ea822..cbcc786af 100644
--- a/weed/storage/needle_map_boltdb.go
+++ b/weed/storage/needle_map_boltdb.go
@@ -7,6 +7,7 @@ import (
 	"github.com/boltdb/bolt"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/storage/needle"
 	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
@@ -31,7 +32,7 @@ func NewBoltDbNeedleMap(dbFileName string, indexFile *os.File) (m *BoltDbNeedleM
 		return
 	}
 	glog.V(1).Infof("Loading %s...", indexFile.Name())
-	nm, indexLoadError := LoadNeedleMap(indexFile)
+	nm, indexLoadError := LoadBtreeNeedleMap(indexFile)
 	if indexLoadError != nil {
 		return nil, indexLoadError
 	}
@@ -72,7 +73,7 @@ func generateBoltDbFile(dbFileName string, indexFile *os.File) error {
 	})
 }
 
-func (m *BoltDbNeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
+func (m *BoltDbNeedleMap) Get(key uint64) (element *needle.NeedleValue, ok bool) {
 	bytes := make([]byte, 8)
 	var data []byte
 	util.Uint64toBytes(bytes, key)
@@ -91,7 +92,7 @@ func (m *BoltDbNeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
 	}
 	offset := util.BytesToUint32(data[0:4])
 	size := util.BytesToUint32(data[4:8])
-	return &NeedleValue{Key: Key(key), Offset: offset, Size: size}, true
+	return &needle.NeedleValue{Key: needle.Key(key), Offset: offset, Size: size}, true
 }
 
 func (m *BoltDbNeedleMap) Put(key uint64, offset uint32, size uint32) error {
diff --git a/weed/storage/needle_map_leveldb.go b/weed/storage/needle_map_leveldb.go
index f025ea360..bd2c7c886 100644
--- a/weed/storage/needle_map_leveldb.go
+++ b/weed/storage/needle_map_leveldb.go
@@ -6,6 +6,7 @@ import (
 	"path/filepath"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/storage/needle"
 	"github.com/chrislusf/seaweedfs/weed/util"
 	"github.com/syndtr/goleveldb/leveldb"
 )
@@ -29,7 +30,7 @@ func NewLevelDbNeedleMap(dbFileName string, indexFile *os.File) (m *LevelDbNeedl
 		return
 	}
 	glog.V(1).Infof("Loading %s...", indexFile.Name())
-	nm, indexLoadError := LoadNeedleMap(indexFile)
+	nm, indexLoadError := LoadBtreeNeedleMap(indexFile)
 	if indexLoadError != nil {
 		return nil, indexLoadError
 	}
@@ -70,7 +71,7 @@ func generateLevelDbFile(dbFileName string, indexFile *os.File) error {
 	})
 }
 
-func (m *LevelDbNeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
+func (m *LevelDbNeedleMap) Get(key uint64) (element *needle.NeedleValue, ok bool) {
 	bytes := make([]byte, 8)
 	util.Uint64toBytes(bytes, key)
 	data, err := m.db.Get(bytes, nil)
@@ -79,7 +80,7 @@ func (m *LevelDbNeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
 	}
 	offset := util.BytesToUint32(data[0:4])
 	size := util.BytesToUint32(data[4:8])
-	return &NeedleValue{Key: Key(key), Offset: offset, Size: size}, true
+	return &needle.NeedleValue{Key: needle.Key(key), Offset: offset, Size: size}, true
 }
 
 func (m *LevelDbNeedleMap) Put(key uint64, offset uint32, size uint32) error {
diff --git a/weed/storage/needle_map_memory.go b/weed/storage/needle_map_memory.go
index ccbb21317..f34a57849 100644
--- a/weed/storage/needle_map_memory.go
+++ b/weed/storage/needle_map_memory.go
@@ -5,17 +5,26 @@ import (
 	"os"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/storage/needle"
 )
 
 type NeedleMap struct {
-	m CompactMap
+	m needle.NeedleValueMap
 
 	baseNeedleMapper
 }
 
-func NewNeedleMap(file *os.File) *NeedleMap {
+func NewCompactNeedleMap(file *os.File) *NeedleMap {
 	nm := &NeedleMap{
-		m: NewCompactMap(),
+		m: needle.NewCompactMap(),
+	}
+	nm.indexFile = file
+	return nm
+}
+
+func NewBtreeNeedleMap(file *os.File) *NeedleMap {
+	nm := &NeedleMap{
+		m: needle.NewBtreeMap(),
 	}
 	nm.indexFile = file
 	return nm
@@ -25,8 +34,17 @@ const (
 	RowsToRead = 1024
 )
 
-func LoadNeedleMap(file *os.File) (*NeedleMap, error) {
-	nm := NewNeedleMap(file)
+func LoadCompactNeedleMap(file *os.File) (*NeedleMap, error) {
+	nm := NewCompactNeedleMap(file)
+	return doLoading(file, nm)
+}
+
+func LoadBtreeNeedleMap(file *os.File) (*NeedleMap, error) {
+	nm := NewBtreeNeedleMap(file)
+	return doLoading(file, nm)
+}
+
+func doLoading(file *os.File, nm *NeedleMap) (*NeedleMap, error) {
 	e := WalkIndexFile(file, func(key uint64, offset, size uint32) error {
 		if key > nm.MaximumFileKey {
 			nm.MaximumFileKey = key
@@ -34,14 +52,14 @@ func LoadNeedleMap(file *os.File) (*NeedleMap, error) {
 		if offset > 0 && size != TombstoneFileSize {
 			nm.FileCounter++
 			nm.FileByteCounter = nm.FileByteCounter + uint64(size)
-			oldOffset, oldSize := nm.m.Set(Key(key), offset, size)
+			oldOffset, oldSize := nm.m.Set(needle.Key(key), offset, size)
 			glog.V(3).Infoln("reading key", key, "offset", offset*NeedlePaddingSize, "size", size, "oldSize", oldSize)
 			if oldOffset > 0 && oldSize != TombstoneFileSize {
 				nm.DeletionCounter++
 				nm.DeletionByteCounter = nm.DeletionByteCounter + uint64(oldSize)
 			}
 		} else {
-			oldSize := nm.m.Delete(Key(key))
+			oldSize := nm.m.Delete(needle.Key(key))
 			glog.V(3).Infoln("removing key", key, "offset", offset*NeedlePaddingSize, "size", size, "oldSize", oldSize)
 			nm.DeletionCounter++
 			nm.DeletionByteCounter = nm.DeletionByteCounter + uint64(oldSize)
@@ -84,16 +102,16 @@ func WalkIndexFile(r *os.File, fn func(key uint64, offset, size uint32) error) e
 }
 
 func (nm *NeedleMap) Put(key uint64, offset uint32, size uint32) error {
-	_, oldSize := nm.m.Set(Key(key), offset, size)
+	_, oldSize := nm.m.Set(needle.Key(key), offset, size)
 	nm.logPut(key, oldSize, size)
 	return nm.appendToIndexFile(key, offset, size)
 }
-func (nm *NeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
-	element, ok = nm.m.Get(Key(key))
+func (nm *NeedleMap) Get(key uint64) (element *needle.NeedleValue, ok bool) {
+	element, ok = nm.m.Get(needle.Key(key))
 	return
 }
 func (nm *NeedleMap) Delete(key uint64, offset uint32) error {
-	deletedBytes := nm.m.Delete(Key(key))
+	deletedBytes := nm.m.Delete(needle.Key(key))
 	nm.logDelete(deletedBytes)
 	return nm.appendToIndexFile(key, offset, TombstoneFileSize)
 }
diff --git a/weed/storage/volume_loading.go b/weed/storage/volume_loading.go
index 4be860987..457d50410 100644
--- a/weed/storage/volume_loading.go
+++ b/weed/storage/volume_loading.go
@@ -70,20 +70,25 @@ func (v *Volume) load(alsoLoadIndex bool, createDatIfMissing bool, needleMapKind
 		}
 		switch needleMapKind {
 		case NeedleMapInMemory:
-			glog.V(0).Infoln("loading index file", fileName+".idx", "readonly", v.readOnly)
-			if v.nm, e = LoadNeedleMap(indexFile); e != nil {
-				glog.V(0).Infof("loading index %s error: %v", fileName+".idx", e)
+			glog.V(0).Infoln("loading index", fileName+".idx", "to memory readonly", v.readOnly)
+			if v.nm, e = LoadCompactNeedleMap(indexFile); e != nil {
+				glog.V(0).Infof("loading index %s to memory error: %v", fileName+".idx", e)
 			}
 		case NeedleMapLevelDb:
-			glog.V(0).Infoln("loading leveldb file", fileName+".ldb")
+			glog.V(0).Infoln("loading leveldb", fileName+".ldb")
 			if v.nm, e = NewLevelDbNeedleMap(fileName+".ldb", indexFile); e != nil {
 				glog.V(0).Infof("loading leveldb %s error: %v", fileName+".ldb", e)
 			}
 		case NeedleMapBoltDb:
-			glog.V(0).Infoln("loading boltdb file", fileName+".bdb")
+			glog.V(0).Infoln("loading boltdb", fileName+".bdb")
 			if v.nm, e = NewBoltDbNeedleMap(fileName+".bdb", indexFile); e != nil {
 				glog.V(0).Infof("loading boltdb %s error: %v", fileName+".bdb", e)
 			}
+		case NeedleMapBtree:
+			glog.V(0).Infoln("loading index", fileName+".idx", "to btree readonly", v.readOnly)
+			if v.nm, e = LoadBtreeNeedleMap(indexFile); e != nil {
+				glog.V(0).Infof("loading index %s to btree error: %v", fileName+".idx", e)
+			}
 		}
 	}
 
diff --git a/weed/storage/volume_sync.go b/weed/storage/volume_sync.go
index 23d8db510..d7cae8803 100644
--- a/weed/storage/volume_sync.go
+++ b/weed/storage/volume_sync.go
@@ -11,6 +11,7 @@ import (
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
 	"github.com/chrislusf/seaweedfs/weed/operation"
+	"github.com/chrislusf/seaweedfs/weed/storage/needle"
 	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
@@ -48,7 +49,7 @@ optimized more later).
 func (v *Volume) Synchronize(volumeServer string) (err error) {
 	var lastCompactRevision uint16 = 0
 	var compactRevision uint16 = 0
-	var masterMap CompactMap
+	var masterMap *needle.CompactMap
 	for i := 0; i < 3; i++ {
 		if masterMap, _, compactRevision, err = fetchVolumeFileEntries(volumeServer, v.Id); err != nil {
 			return fmt.Errorf("Failed to sync volume %d entries with %s: %v", v.Id, volumeServer, err)
@@ -69,7 +70,7 @@ func (v *Volume) Synchronize(volumeServer string) (err error) {
 	return
 }
 
-type ByOffset []NeedleValue
+type ByOffset []needle.NeedleValue
 
 func (a ByOffset) Len() int           { return len(a) }
 func (a ByOffset) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
@@ -77,18 +78,18 @@ func (a ByOffset) Less(i, j int) bool { return a[i].Offset < a[j].Offset }
 
 // trySynchronizing sync with remote volume server incrementally by
 // make up the local and remote delta.
-func (v *Volume) trySynchronizing(volumeServer string, masterMap CompactMap, compactRevision uint16) error {
+func (v *Volume) trySynchronizing(volumeServer string, masterMap *needle.CompactMap, compactRevision uint16) error {
 	slaveIdxFile, err := os.Open(v.nm.IndexFileName())
 	if err != nil {
 		return fmt.Errorf("Open volume %d index file: %v", v.Id, err)
 	}
 	defer slaveIdxFile.Close()
-	slaveMap, err := LoadNeedleMap(slaveIdxFile)
+	slaveMap, err := LoadBtreeNeedleMap(slaveIdxFile)
 	if err != nil {
 		return fmt.Errorf("Load volume %d index file: %v", v.Id, err)
 	}
-	var delta []NeedleValue
-	if err := masterMap.Visit(func(needleValue NeedleValue) error {
+	var delta []needle.NeedleValue
+	if err := masterMap.Visit(func(needleValue needle.NeedleValue) error {
 		if needleValue.Key == 0 {
 			return nil
 		}
@@ -100,7 +101,7 @@ func (v *Volume) trySynchronizing(volumeServer string, masterMap CompactMap, com
 	}); err != nil {
 		return fmt.Errorf("Add master entry: %v", err)
 	}
-	if err := slaveMap.m.Visit(func(needleValue NeedleValue) error {
+	if err := slaveMap.m.Visit(func(needleValue needle.NeedleValue) error {
 		if needleValue.Key == 0 {
 			return nil
 		}
@@ -137,8 +138,8 @@ func (v *Volume) trySynchronizing(volumeServer string, masterMap CompactMap, com
 	return nil
 }
 
-func fetchVolumeFileEntries(volumeServer string, vid VolumeId) (m CompactMap, lastOffset uint64, compactRevision uint16, err error) {
-	m = NewCompactMap()
+func fetchVolumeFileEntries(volumeServer string, vid VolumeId) (m *needle.CompactMap, lastOffset uint64, compactRevision uint16, err error) {
+	m = needle.NewCompactMap()
 
 	syncStatus, err := operation.GetVolumeSyncStatus(volumeServer, vid.String())
 	if err != nil {
@@ -149,9 +150,9 @@ func fetchVolumeFileEntries(volumeServer string, vid VolumeId) (m CompactMap, la
 	err = operation.GetVolumeIdxEntries(volumeServer, vid.String(), func(key uint64, offset, size uint32) {
 		// println("remote key", key, "offset", offset*NeedlePaddingSize, "size", size)
 		if offset > 0 && size != TombstoneFileSize {
-			m.Set(Key(key), offset, size)
+			m.Set(needle.Key(key), offset, size)
 		} else {
-			m.Delete(Key(key))
+			m.Delete(needle.Key(key))
 		}
 		total++
 	})
@@ -178,7 +179,7 @@ func (v *Volume) IndexFileContent() ([]byte, error) {
 }
 
 // removeNeedle removes one needle by needle key
-func (v *Volume) removeNeedle(key Key) {
+func (v *Volume) removeNeedle(key needle.Key) {
 	n := new(Needle)
 	n.Id = uint64(key)
 	v.deleteNeedle(n)
@@ -188,7 +189,7 @@ func (v *Volume) removeNeedle(key Key) {
 // The compact revision is checked first in case the remote volume
 // is compacted and the offset is invalid any more.
 func (v *Volume) fetchNeedle(volumeDataContentHandlerUrl string,
-	needleValue NeedleValue, compactRevision uint16) error {
+	needleValue needle.NeedleValue, compactRevision uint16) error {
 	// add master file entry to local data file
 	values := make(url.Values)
 	values.Add("revision", strconv.Itoa(int(compactRevision)))
diff --git a/weed/storage/volume_vacuum.go b/weed/storage/volume_vacuum.go
index 07916fe6b..f6f68d59b 100644
--- a/weed/storage/volume_vacuum.go
+++ b/weed/storage/volume_vacuum.go
@@ -221,7 +221,7 @@ func (v *Volume) copyDataAndGenerateIndexFile(dstName, idxName string, prealloca
 	}
 	defer idx.Close()
 
-	nm := NewNeedleMap(idx)
+	nm := NewBtreeNeedleMap(idx)
 	new_offset := int64(SuperBlockSize)
 
 	now := uint64(time.Now().Unix())
@@ -272,7 +272,7 @@ func (v *Volume) copyDataBasedOnIndexFile(dstName, idxName string) (err error) {
 	}
 	defer oldIndexFile.Close()
 
-	nm := NewNeedleMap(idx)
+	nm := NewBtreeNeedleMap(idx)
 	now := uint64(time.Now().Unix())
 
 	v.SuperBlock.CompactRevision++