diff --git a/unmaintained/change_superblock/change_superblock.go b/unmaintained/change_superblock/change_superblock.go
index afe651c4e..56342a0cb 100644
--- a/unmaintained/change_superblock/change_superblock.go
+++ b/unmaintained/change_superblock/change_superblock.go
@@ -92,7 +92,7 @@ func main() {
 
 		header := superBlock.Bytes()
 
-		if n, e := datFile.WriteAt(header, 0); n == 0 || e != nil {
+		if n, e := datBackend.WriteAt(header, 0); n == 0 || e != nil {
 			glog.Fatalf("cannot write super block: %v", e)
 		}
 
diff --git a/weed/storage/backend/disk_file.go b/weed/storage/backend/disk_file.go
index 2b04c8df2..498963c31 100644
--- a/weed/storage/backend/disk_file.go
+++ b/weed/storage/backend/disk_file.go
@@ -1,6 +1,8 @@
 package backend
 
 import (
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	. "github.com/chrislusf/seaweedfs/weed/storage/types"
 	"os"
 	"time"
 )
@@ -12,12 +14,25 @@ var (
 type DiskFile struct {
 	File         *os.File
 	fullFilePath string
+	fileSize     int64
+	modTime      time.Time
 }
 
 func NewDiskFile(f *os.File) *DiskFile {
+	stat, err := f.Stat()
+	if err != nil {
+		glog.Fatalf("stat file %s: %v", f.Name(), err)
+	}
+	offset := stat.Size()
+	if offset%NeedlePaddingSize != 0 {
+		offset = offset + (NeedlePaddingSize - offset%NeedlePaddingSize)
+	}
+
 	return &DiskFile{
 		fullFilePath: f.Name(),
 		File:         f,
+		fileSize:     offset,
+		modTime:      stat.ModTime(),
 	}
 }
 
@@ -26,11 +41,28 @@ func (df *DiskFile) ReadAt(p []byte, off int64) (n int, err error) {
 }
 
 func (df *DiskFile) WriteAt(p []byte, off int64) (n int, err error) {
-	return df.File.WriteAt(p, off)
+	n, err = df.File.WriteAt(p, off)
+	if err == nil {
+		waterMark := off + int64(n)
+		if waterMark > df.fileSize {
+			df.fileSize = waterMark
+			df.modTime = time.Now()
+		}
+	}
+	return
+}
+
+func (df *DiskFile) Append(p []byte) (n int, err error) {
+	return df.WriteAt(p, df.fileSize)
 }
 
 func (df *DiskFile) Truncate(off int64) error {
-	return df.File.Truncate(off)
+	err := df.File.Truncate(off)
+	if err == nil {
+		df.fileSize = off
+		df.modTime = time.Now()
+	}
+	return err
 }
 
 func (df *DiskFile) Close() error {
@@ -38,11 +70,7 @@ func (df *DiskFile) Close() error {
 }
 
 func (df *DiskFile) GetStat() (datSize int64, modTime time.Time, err error) {
-	stat, e := df.File.Stat()
-	if e == nil {
-		return stat.Size(), stat.ModTime(), nil
-	}
-	return 0, time.Time{}, err
+	return df.fileSize, df.modTime, nil
 }
 
 func (df *DiskFile) Name() string {
diff --git a/weed/storage/needle/needle_read_write.go b/weed/storage/needle/needle_read_write.go
index e758a6fee..0f72bc0bb 100644
--- a/weed/storage/needle/needle_read_write.go
+++ b/weed/storage/needle/needle_read_write.go
@@ -161,7 +161,15 @@ func ReadNeedleBlob(r backend.BackendStorageFile, offset int64, size Size, versi
 	dataSize := GetActualSize(size, version)
 	dataSlice = make([]byte, int(dataSize))
 
-	_, err = r.ReadAt(dataSlice, offset)
+	var n int
+	n, err = r.ReadAt(dataSlice, offset)
+	if err != nil && int64(n) == dataSize {
+		err = nil
+	}
+	if err != nil {
+		fileSize, _, _ := r.GetStat()
+		println("n",n, "dataSize", dataSize, "offset", offset, "fileSize", fileSize)
+	}
 	return dataSlice, err
 
 }
diff --git a/weed/storage/needle/needle_read_write_test.go b/weed/storage/needle/needle_read_write_test.go
index 47582dd26..afcea5a05 100644
--- a/weed/storage/needle/needle_read_write_test.go
+++ b/weed/storage/needle/needle_read_write_test.go
@@ -48,7 +48,7 @@ func TestAppend(t *testing.T) {
 		int64  : -9223372036854775808 to 9223372036854775807
 	*/
 
-	fileSize := int64(4294967295) + 10000
+	fileSize := int64(4294967296) + 10000
 	tempFile.Truncate(fileSize)
 	defer func() {
 		tempFile.Close()
diff --git a/weed/storage/needle_map.go b/weed/storage/needle_map.go
index 5b41286ea..d35391f66 100644
--- a/weed/storage/needle_map.go
+++ b/weed/storage/needle_map.go
@@ -1,7 +1,6 @@
 package storage
 
 import (
-	"fmt"
 	"io"
 	"os"
 	"sync"
@@ -41,6 +40,7 @@ type baseNeedleMapper struct {
 
 	indexFile           *os.File
 	indexFileAccessLock sync.Mutex
+	indexFileOffset     int64
 }
 
 func (nm *baseNeedleMapper) IndexFileSize() uint64 {
@@ -56,11 +56,10 @@ func (nm *baseNeedleMapper) appendToIndexFile(key NeedleId, offset Offset, size
 
 	nm.indexFileAccessLock.Lock()
 	defer nm.indexFileAccessLock.Unlock()
-	if _, err := nm.indexFile.Seek(0, 2); err != nil {
-		return fmt.Errorf("cannot seek end of indexfile %s: %v",
-			nm.indexFile.Name(), err)
+	written, err := nm.indexFile.WriteAt(bytes, nm.indexFileOffset)
+	if err == nil {
+		nm.indexFileOffset += int64(written)
 	}
-	_, err := nm.indexFile.Write(bytes)
 	return err
 }
 
diff --git a/weed/storage/needle_map_leveldb.go b/weed/storage/needle_map_leveldb.go
index 415cd14dd..9716e9729 100644
--- a/weed/storage/needle_map_leveldb.go
+++ b/weed/storage/needle_map_leveldb.go
@@ -31,6 +31,11 @@ func NewLevelDbNeedleMap(dbFileName string, indexFile *os.File, opts *opt.Option
 		generateLevelDbFile(dbFileName, indexFile)
 		glog.V(1).Infof("Finished Generating %s from %s", dbFileName, indexFile.Name())
 	}
+	if stat, err := indexFile.Stat(); err != nil {
+		glog.Fatalf("stat file %s: %v", indexFile.Name(), err)
+	} else {
+		m.indexFileOffset = stat.Size()
+	}
 	glog.V(1).Infof("Opening %s...", dbFileName)
 
 	if m.db, err = leveldb.OpenFile(dbFileName, opts); err != nil {
diff --git a/weed/storage/needle_map_memory.go b/weed/storage/needle_map_memory.go
index d0891dc98..1b58708c6 100644
--- a/weed/storage/needle_map_memory.go
+++ b/weed/storage/needle_map_memory.go
@@ -19,6 +19,11 @@ func NewCompactNeedleMap(file *os.File) *NeedleMap {
 		m: needle_map.NewCompactMap(),
 	}
 	nm.indexFile = file
+	stat, err := file.Stat()
+	if err != nil {
+		glog.Fatalf("stat file %s: %v", file.Name(), err)
+	}
+	nm.indexFileOffset = stat.Size()
 	return nm
 }
 
diff --git a/weed/storage/volume_vacuum.go b/weed/storage/volume_vacuum.go
index c17c9c937..0ee1e61c6 100644
--- a/weed/storage/volume_vacuum.go
+++ b/weed/storage/volume_vacuum.go
@@ -286,7 +286,7 @@ func (v *Volume) makeupDiff(newDatFileName, newIdxFileName, oldDatFileName, oldI
 			if err != nil {
 				return fmt.Errorf("ReadNeedleBlob %s key %d offset %d size %d failed: %v", oldDatFile.Name(), key, increIdxEntry.offset.ToActualOffset(), increIdxEntry.size, err)
 			}
-			dst.Write(needleBytes)
+			dstDatBackend.Append(needleBytes)
 			util.Uint32toBytes(idxEntryBytes[8:12], uint32(offset/NeedlePaddingSize))
 		} else { //deleted needle
 			//fakeDelNeedle 's default Data field is nil