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 161f4ca83..498963c31 100644
--- a/weed/storage/backend/disk_file.go
+++ b/weed/storage/backend/disk_file.go
@@ -2,6 +2,7 @@ package backend
 
 import (
 	"github.com/chrislusf/seaweedfs/weed/glog"
+	. "github.com/chrislusf/seaweedfs/weed/storage/types"
 	"os"
 	"time"
 )
@@ -22,11 +23,15 @@ func NewDiskFile(f *os.File) *DiskFile {
 	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:     stat.Size(),
+		fileSize:     offset,
 		modTime:      stat.ModTime(),
 	}
 }
@@ -47,6 +52,10 @@ func (df *DiskFile) WriteAt(p []byte, off int64) (n int, err error) {
 	return
 }
 
+func (df *DiskFile) Append(p []byte) (n int, err error) {
+	return df.WriteAt(p, df.fileSize)
+}
+
 func (df *DiskFile) Truncate(off int64) error {
 	err := df.File.Truncate(off)
 	if err == nil {
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