diff --git a/weed/storage/volume_vacuum.go b/weed/storage/volume_vacuum.go
index d8141cf71..bbe17071e 100644
--- a/weed/storage/volume_vacuum.go
+++ b/weed/storage/volume_vacuum.go
@@ -236,15 +236,13 @@ func (v *Volume) makeupDiff(newDatFileName, newIdxFileName, oldDatFileName, oldI
 }
 
 type VolumeFileScanner4Vacuum struct {
-	version                 needle.Version
-	v                       *Volume
-	dst                     *os.File
-	nm                      *NeedleMap
-	newOffset               int64
-	now                     uint64
-	compactionBytePerSecond int64
-	lastSizeCounter         int64
-	lastSizeCheckTime       time.Time
+	version        needle.Version
+	v              *Volume
+	dst            *os.File
+	nm             *NeedleMap
+	newOffset      int64
+	now            uint64
+	writeThrottler *util.WriteThrottler
 }
 
 func (scanner *VolumeFileScanner4Vacuum) VisitSuperBlock(superBlock SuperBlock) error {
@@ -274,28 +272,11 @@ func (scanner *VolumeFileScanner4Vacuum) VisitNeedle(n *needle.Needle, offset in
 		}
 		delta := n.DiskSize(scanner.version)
 		scanner.newOffset += delta
-		scanner.maybeSlowdown(delta)
+		scanner.writeThrottler.MaybeSlowdown(delta)
 		glog.V(4).Infoln("saving key", n.Id, "volume offset", offset, "=>", scanner.newOffset, "data_size", n.Size)
 	}
 	return nil
 }
-func (scanner *VolumeFileScanner4Vacuum) maybeSlowdown(delta int64) {
-	if scanner.compactionBytePerSecond > 0 {
-		scanner.lastSizeCounter += delta
-		now := time.Now()
-		elapsedDuration := now.Sub(scanner.lastSizeCheckTime)
-		if elapsedDuration > 100*time.Millisecond {
-			overLimitBytes := scanner.lastSizeCounter - scanner.compactionBytePerSecond/10
-			if overLimitBytes > 0 {
-				overRatio := float64(overLimitBytes) / float64(scanner.compactionBytePerSecond)
-				sleepTime := time.Duration(overRatio*1000) * time.Millisecond
-				// glog.V(0).Infof("currently %d bytes, limit to %d bytes, over by %d bytes, sleeping %v over %.4f", scanner.lastSizeCounter, scanner.compactionBytePerSecond/10, overLimitBytes, sleepTime, overRatio)
-				time.Sleep(sleepTime)
-			}
-			scanner.lastSizeCounter, scanner.lastSizeCheckTime = 0, time.Now()
-		}
-	}
-}
 
 func (v *Volume) copyDataAndGenerateIndexFile(dstName, idxName string, preallocate int64, compactionBytePerSecond int64) (err error) {
 	var (
@@ -312,12 +293,11 @@ func (v *Volume) copyDataAndGenerateIndexFile(dstName, idxName string, prealloca
 	defer idx.Close()
 
 	scanner := &VolumeFileScanner4Vacuum{
-		v:                       v,
-		now:                     uint64(time.Now().Unix()),
-		nm:                      NewBtreeNeedleMap(idx),
-		dst:                     dst,
-		compactionBytePerSecond: compactionBytePerSecond,
-		lastSizeCheckTime:       time.Now(),
+		v:              v,
+		now:            uint64(time.Now().Unix()),
+		nm:             NewBtreeNeedleMap(idx),
+		dst:            dst,
+		writeThrottler: util.NewWriteThrottler(compactionBytePerSecond),
 	}
 	err = ScanVolumeFile(v.dir, v.Collection, v.Id, v.needleMapKind, scanner)
 	return
diff --git a/weed/util/throttler.go b/weed/util/throttler.go
new file mode 100644
index 000000000..873161e37
--- /dev/null
+++ b/weed/util/throttler.go
@@ -0,0 +1,34 @@
+package util
+
+import "time"
+
+type WriteThrottler struct {
+	compactionBytePerSecond int64
+	lastSizeCounter         int64
+	lastSizeCheckTime       time.Time
+}
+
+func NewWriteThrottler(bytesPerSecond int64) *WriteThrottler {
+	return &WriteThrottler{
+		compactionBytePerSecond: bytesPerSecond,
+		lastSizeCheckTime:       time.Now(),
+	}
+}
+
+func (wt *WriteThrottler) MaybeSlowdown(delta int64) {
+	if wt.compactionBytePerSecond > 0 {
+		wt.lastSizeCounter += delta
+		now := time.Now()
+		elapsedDuration := now.Sub(wt.lastSizeCheckTime)
+		if elapsedDuration > 100*time.Millisecond {
+			overLimitBytes := wt.lastSizeCounter - wt.compactionBytePerSecond/10
+			if overLimitBytes > 0 {
+				overRatio := float64(overLimitBytes) / float64(wt.compactionBytePerSecond)
+				sleepTime := time.Duration(overRatio*1000) * time.Millisecond
+				// glog.V(0).Infof("currently %d bytes, limit to %d bytes, over by %d bytes, sleeping %v over %.4f", wt.lastSizeCounter, wt.compactionBytePerSecond/10, overLimitBytes, sleepTime, overRatio)
+				time.Sleep(sleepTime)
+			}
+			wt.lastSizeCounter, wt.lastSizeCheckTime = 0, time.Now()
+		}
+	}
+}