diff --git a/Makefile b/Makefile
index 6719a7bdd..68bd916be 100644
--- a/Makefile
+++ b/Makefile
@@ -20,3 +20,6 @@ build: deps
 linux: deps
 	mkdir -p linux
 	GOOS=linux GOARCH=amd64 go build $(GO_FLAGS) -o linux/$(BINARY) $(SOURCE_DIR)
+
+imports:
+	goimports -w $(SOURCE_DIR)
\ No newline at end of file
diff --git a/go/filer/flat_namespace/flat_namespace_store.go b/go/filer/flat_namespace/flat_namespace_store.go
index 832b70e40..068201adf 100644
--- a/go/filer/flat_namespace/flat_namespace_store.go
+++ b/go/filer/flat_namespace/flat_namespace_store.go
@@ -1,7 +1,5 @@
 package flat_namespace
 
-import ()
-
 type FlatNamespaceStore interface {
 	Put(fullFileName string, fid string) (err error)
 	Get(fullFileName string) (fid string, err error)
diff --git a/go/storage/needle_read_write.go b/go/storage/needle_read_write.go
index daab6121f..751c6d797 100644
--- a/go/storage/needle_read_write.go
+++ b/go/storage/needle_read_write.go
@@ -238,13 +238,25 @@ func (n *Needle) ReadNeedleBody(r *os.File, version Version, offset int64, bodyL
 		}
 		n.Data = bytes[:n.Size]
 		n.Checksum = NewCRC(n.Data)
+		checksum := binary.BigEndian.Uint32(bytes[n.Size : n.Size+NeedleChecksumSize])
+
+		if n.Checksum.Value() != checksum {
+			glog.V(0).Infof("CRC error! Data On Disk Corrupted, needle id = %x", n.Id)
+		}
 	case Version2:
 		bytes := make([]byte, bodyLength)
 		if _, err = r.ReadAt(bytes, offset); err != nil {
 			return
 		}
 		n.readNeedleDataVersion2(bytes[0:n.Size])
+		if n.DataSize == 0 {
+			return
+		}
 		n.Checksum = NewCRC(n.Data)
+		checksum := binary.BigEndian.Uint32(bytes[n.Size : n.Size+NeedleChecksumSize])
+		if n.Checksum.Value() != checksum {
+			glog.V(0).Infof("CRC error! Data On Disk Corrupted, needle id = %x", n.Id)
+		}
 	default:
 		err = fmt.Errorf("Unsupported Version! (%d)", version)
 	}
diff --git a/go/storage/volume_info.go b/go/storage/volume_info.go
index a2f139c89..e4979c790 100644
--- a/go/storage/volume_info.go
+++ b/go/storage/volume_info.go
@@ -2,8 +2,9 @@ package storage
 
 import (
 	"fmt"
-	"github.com/chrislusf/seaweedfs/go/operation"
 	"sort"
+
+	"github.com/chrislusf/seaweedfs/go/operation"
 )
 
 type VolumeInfo struct {
diff --git a/go/storage/volume_replicate.go b/go/storage/volume_replicate.go
new file mode 100644
index 000000000..e85bdc417
--- /dev/null
+++ b/go/storage/volume_replicate.go
@@ -0,0 +1,212 @@
+package storage
+
+import (
+	"io"
+	"os"
+	"sort"
+	"sync"
+
+	"encoding/binary"
+)
+
+type DirtyData struct {
+	Offset int64  `comment:"Dirty data start offset"`
+	Size   uint32 `comment:"Size of the dirty data"`
+}
+
+type DirtyDatas []DirtyData
+
+func (s DirtyDatas) Len() int           { return len(s) }
+func (s DirtyDatas) Less(i, j int) bool { return s[i].Offset < s[j].Offset }
+func (s DirtyDatas) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s DirtyDatas) Sort()              { sort.Sort(s) }
+func (s DirtyDatas) Search(offset int64) int {
+	return sort.Search(len(s), func(i int) bool {
+		v := &s[i]
+		return v.Offset+int64(v.Size) > offset
+	})
+}
+
+type CleanReader struct {
+	Dirtys   DirtyDatas
+	DataFile *os.File
+	pr       *io.PipeReader
+	pw       *io.PipeWriter
+	mutex    sync.Mutex
+}
+
+func ScanDirtyData(indexFileContent []byte) (dirtys DirtyDatas) {
+	m := NewCompactMap()
+	for i := 0; i+16 <= len(indexFileContent); i += 16 {
+		bytes := indexFileContent[i : i+16]
+		key := binary.BigEndian.Uint64(bytes[:8])
+		offset := binary.BigEndian.Uint32(bytes[8:12])
+		size := binary.BigEndian.Uint32(bytes[12:16])
+		k := Key(key)
+		if offset != 0 && size != 0 {
+			m.Set(k, offset, size)
+		} else {
+			if nv, ok := m.Get(k); ok {
+				//mark old needle data as dirty data
+				if int64(nv.Size)-NeedleHeaderSize > 0 {
+					dirtys = append(dirtys, DirtyData{
+						Offset: int64(nv.Offset)*8 + NeedleHeaderSize,
+						Size:   nv.Size,
+					})
+				}
+			}
+			m.Delete(k)
+		}
+	}
+	dirtys.Sort()
+	return dirtys
+}
+
+func (cr *CleanReader) Seek(offset int64, whence int) (int64, error) {
+	oldOff, e := cr.DataFile.Seek(0, 1)
+	if e != nil {
+		return 0, e
+	}
+	newOff, e := cr.DataFile.Seek(offset, whence)
+	if e != nil {
+		return 0, e
+	}
+	if oldOff != newOff {
+		cr.closePipe(true)
+	}
+	return newOff, nil
+}
+
+func (cr *CleanReader) Size() (int64, error) {
+	fi, e := cr.DataFile.Stat()
+	if e != nil {
+		return 0, e
+	}
+	return fi.Size(), nil
+}
+
+func (cdr *CleanReader) WriteTo(w io.Writer) (written int64, err error) {
+	off, e := cdr.DataFile.Seek(0, 1)
+	if e != nil {
+		return 0, nil
+	}
+	const ZeroBufSize = 32 * 1024
+	zeroBuf := make([]byte, ZeroBufSize)
+	dirtyIndex := cdr.Dirtys.Search(off)
+	var nextDirty *DirtyData
+	if dirtyIndex < len(cdr.Dirtys) {
+		nextDirty = &cdr.Dirtys[dirtyIndex]
+	}
+	for {
+		if nextDirty != nil && off >= nextDirty.Offset && off < nextDirty.Offset+int64(nextDirty.Size) {
+			sz := nextDirty.Offset + int64(nextDirty.Size) - off
+			for sz > 0 {
+				mn := int64(ZeroBufSize)
+				if mn > sz {
+					mn = sz
+				}
+				var n int
+				if n, e = w.Write(zeroBuf[:mn]); e != nil {
+					return
+				}
+				written += int64(n)
+				sz -= int64(n)
+				off += int64(n)
+			}
+			dirtyIndex++
+			if dirtyIndex < len(cdr.Dirtys) {
+				nextDirty = &cdr.Dirtys[dirtyIndex]
+			} else {
+				nextDirty = nil
+			}
+			if _, e = cdr.DataFile.Seek(off, 0); e != nil {
+				return
+			}
+		} else {
+			var n, sz int64
+			if nextDirty != nil {
+				sz = nextDirty.Offset - off
+			}
+			if sz <= 0 {
+				// copy until eof
+				n, e = io.Copy(w, cdr.DataFile)
+				written += n
+				return
+			}
+			if n, e = io.CopyN(w, cdr.DataFile, sz); e != nil {
+				return
+			}
+			off += n
+			written += n
+		}
+	}
+	return
+}
+
+func (cr *CleanReader) ReadAt(p []byte, off int64) (n int, err error) {
+	cr.Seek(off, 0)
+	return cr.Read(p)
+}
+
+func (cr *CleanReader) Read(p []byte) (int, error) {
+	return cr.getPipeReader().Read(p)
+}
+
+func (cr *CleanReader) Close() (e error) {
+	cr.closePipe(true)
+	return cr.DataFile.Close()
+}
+
+func (cr *CleanReader) closePipe(lock bool) (e error) {
+	if lock {
+		cr.mutex.Lock()
+		defer cr.mutex.Unlock()
+	}
+	if cr.pr != nil {
+		if err := cr.pr.Close(); err != nil {
+			e = err
+		}
+	}
+	cr.pr = nil
+	if cr.pw != nil {
+		if err := cr.pw.Close(); err != nil {
+			e = err
+		}
+	}
+	cr.pw = nil
+	return e
+}
+
+func (cr *CleanReader) getPipeReader() io.Reader {
+	cr.mutex.Lock()
+	defer cr.mutex.Unlock()
+	if cr.pr != nil && cr.pw != nil {
+		return cr.pr
+	}
+	cr.closePipe(false)
+	cr.pr, cr.pw = io.Pipe()
+	go func(pw *io.PipeWriter) {
+		_, e := cr.WriteTo(pw)
+		pw.CloseWithError(e)
+	}(cr.pw)
+	return cr.pr
+}
+
+func (v *Volume) GetVolumeCleanReader() (cr *CleanReader, err error) {
+	var dirtys DirtyDatas
+	if indexData, e := v.nm.IndexFileContent(); e != nil {
+		return nil, err
+	} else {
+		dirtys = ScanDirtyData(indexData)
+	}
+	dataFile, e := os.Open(v.FileName() + ".dat")
+
+	if e != nil {
+		return nil, e
+	}
+	cr = &CleanReader{
+		Dirtys:   dirtys,
+		DataFile: dataFile,
+	}
+	return
+}
diff --git a/go/storage/volume_replicate_test.go b/go/storage/volume_replicate_test.go
new file mode 100644
index 000000000..d1da211c3
--- /dev/null
+++ b/go/storage/volume_replicate_test.go
@@ -0,0 +1,22 @@
+package storage
+
+import "testing"
+
+func TestDirtyDataSearch(t *testing.T) {
+	testData := DirtyDatas{
+		{30, 20}, {106, 200}, {5, 20}, {512, 68}, {412, 50},
+	}
+	testOffset := []int64{
+		0, 150, 480, 1024,
+	}
+	testData.Sort()
+	t.Logf("TestData = %v", testData)
+	for _, off := range testOffset {
+		i := testData.Search(off)
+		if i < testData.Len() {
+			t.Logf("(%d) nearest chunk[%d]: %v", off, i, testData[i])
+		} else {
+			t.Logf("Search %d return %d ", off, i)
+		}
+	}
+}
diff --git a/go/storage/volume_sync.go b/go/storage/volume_sync.go
index 2c72d62f0..01d59d6ae 100644
--- a/go/storage/volume_sync.go
+++ b/go/storage/volume_sync.go
@@ -202,6 +202,9 @@ func (v *Volume) fetchNeedle(volumeDataContentHandlerUrl string,
 		if err != nil {
 			return fmt.Errorf("Reading from %s error: %v", volumeDataContentHandlerUrl, err)
 		}
+		if needleValue.Size != uint32(len(b)) {
+			return fmt.Errorf("Reading from %s error: size incorrect", volumeDataContentHandlerUrl)
+		}
 		offset, err := v.AppendBlob(b)
 		if err != nil {
 			return fmt.Errorf("Appending volume %d error: %v", v.Id, err)
diff --git a/go/weed/weed_server/volume_server.go b/go/weed/weed_server/volume_server.go
index 8becdd0f1..b8472235e 100644
--- a/go/weed/weed_server/volume_server.go
+++ b/go/weed/weed_server/volume_server.go
@@ -57,6 +57,7 @@ func NewVolumeServer(adminMux, publicMux *http.ServeMux, ip string,
 	adminMux.HandleFunc("/admin/sync/status", vs.guard.WhiteList(vs.getVolumeSyncStatusHandler))
 	adminMux.HandleFunc("/admin/sync/index", vs.guard.WhiteList(vs.getVolumeIndexContentHandler))
 	adminMux.HandleFunc("/admin/sync/data", vs.guard.WhiteList(vs.getVolumeDataContentHandler))
+	adminMux.HandleFunc("/admin/sync/vol_data", vs.guard.WhiteList(vs.getVolumeCleanDataHandler))
 	adminMux.HandleFunc("/stats/counter", vs.guard.WhiteList(statsCounterHandler))
 	adminMux.HandleFunc("/stats/memory", vs.guard.WhiteList(statsMemoryHandler))
 	adminMux.HandleFunc("/stats/disk", vs.guard.WhiteList(vs.statsDiskHandler))
diff --git a/go/weed/weed_server/volume_server_handlers_replicate.go b/go/weed/weed_server/volume_server_handlers_replicate.go
new file mode 100644
index 000000000..411967326
--- /dev/null
+++ b/go/weed/weed_server/volume_server_handlers_replicate.go
@@ -0,0 +1,66 @@
+package weed_server
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"strconv"
+
+	"github.com/chrislusf/seaweedfs/go/glog"
+	"github.com/pierrec/lz4"
+)
+
+func (vs *VolumeServer) getVolumeCleanDataHandler(w http.ResponseWriter, r *http.Request) {
+	v, e := vs.getVolume("volume", r)
+	if v == nil {
+		http.Error(w, fmt.Sprintf("Not Found volume: %v", e), http.StatusBadRequest)
+		return
+	}
+	cr, e := v.GetVolumeCleanReader()
+	if e != nil {
+		http.Error(w, fmt.Sprintf("Get volume clean reader: %v", e), http.StatusInternalServerError)
+		return
+	}
+	totalSize, e := cr.Size()
+	if e != nil {
+		http.Error(w, fmt.Sprintf("Get volume size: %v", e), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Accept-Ranges", "bytes")
+	w.Header().Set("Content-Disposition", fmt.Sprintf(`filename="%d.dat.lz4"`, v.Id))
+
+	rangeReq := r.Header.Get("Range")
+	if rangeReq == "" {
+		w.Header().Set("Content-Length", strconv.FormatInt(totalSize, 10))
+		w.Header().Set("Content-Encoding", "lz4")
+		lz4w := lz4.NewWriter(w)
+		if _, e = io.Copy(lz4w, cr); e != nil {
+			glog.V(4).Infoln("response write error:", e)
+		}
+		lz4w.Close()
+		return
+	}
+	ranges, e := parseRange(rangeReq, totalSize)
+	if e != nil {
+		http.Error(w, e.Error(), http.StatusRequestedRangeNotSatisfiable)
+		return
+	}
+	if len(ranges) != 1 {
+		http.Error(w, "Only support one range", http.StatusNotImplemented)
+		return
+	}
+	ra := ranges[0]
+	if _, e := cr.Seek(ra.start, 0); e != nil {
+		http.Error(w, e.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Length", strconv.FormatInt(ra.length, 10))
+	w.Header().Set("Content-Range", ra.contentRange(totalSize))
+	w.Header().Set("Content-Encoding", "lz4")
+	w.WriteHeader(http.StatusPartialContent)
+	lz4w := lz4.NewWriter(w)
+	if _, e = io.CopyN(lz4w, cr, ra.length); e != nil {
+		glog.V(2).Infoln("response write error:", e)
+	}
+	lz4w.Close()
+}