diff --git a/weed-fs/src/cmd/weed/fix.go b/weed-fs/src/cmd/weed/fix.go
index d794374cb..deee9a81f 100644
--- a/weed-fs/src/cmd/weed/fix.go
+++ b/weed-fs/src/cmd/weed/fix.go
@@ -50,20 +50,28 @@ func runFix(cmd *Command, args []string) bool {
 		log.Fatalf("cannot read superblock: %s", e)
 	}
 
-	ver, _, _ := storage.ParseSuperBlock(header)
+	ver, _, e := storage.ParseSuperBlock(header)
+	if e != nil {
+		log.Fatalf("error parsing superblock: %s", e)
+	}
 
-	n, rest := storage.ReadNeedleHeader(dataFile, ver)
+	n, rest, e := storage.ReadNeedleHeader(dataFile, ver)
+	if e != nil {
+		log.Fatalf("error reading needle header: %s", e)
+	}
 	dataFile.Seek(int64(rest), 1)
 	nm := storage.NewNeedleMap(indexFile)
 	offset := uint32(storage.SuperBlockSize)
 	for n != nil {
 		debug("key", n.Id, "volume offset", offset, "data_size", n.Size, "rest", rest)
 		if n.Size > 0 {
-			count, pe := nm.Put(n.Id, offset/8, n.Size)
+			count, pe := nm.Put(n.Id, offset/storage.NeedlePaddingSize, n.Size)
 			debug("saved", count, "with error", pe)
 		}
 		offset += rest + 16
-		n, rest = storage.ReadNeedleHeader(dataFile, ver)
+		if n, rest, e = storage.ReadNeedleHeader(dataFile, ver); e != nil {
+			log.Fatalf("error reading needle header: %s", e)
+		}
 		dataFile.Seek(int64(rest), 1)
 	}
 	return true
diff --git a/weed-fs/src/cmd/weed/volume.go b/weed-fs/src/cmd/weed/volume.go
index 4ee8c31a5..ee569843f 100644
--- a/weed-fs/src/cmd/weed/volume.go
+++ b/weed-fs/src/cmd/weed/volume.go
@@ -176,10 +176,12 @@ func PostHandler(w http.ResponseWriter, r *http.Request) {
 		if ne != nil {
 			writeJson(w, r, ne)
 		} else {
-			ret := store.Write(volumeId, needle)
+			ret, err := store.Write(volumeId, needle)
 			errorStatus := ""
 			needToReplicate := !store.HasVolume(volumeId)
-			if ret > 0 {
+			if err != nil {
+				errorStatus = "Failed to write to local disk (" + err.Error() + ")"
+			} else if ret > 0 {
 				needToReplicate = needToReplicate || store.GetVolume(volumeId).NeedToReplicate()
 			} else {
 				errorStatus = "Failed to write to local disk"
@@ -238,7 +240,11 @@ func DeleteHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	n.Size = 0
-	ret := store.Delete(volumeId, n)
+	ret, err := store.Delete(volumeId, n)
+	if err != nil {
+		log.Println("delete error: %s", err)
+		return
+	}
 
 	needToReplicate := !store.HasVolume(volumeId)
 	if !needToReplicate && ret > 0 {
diff --git a/weed-fs/src/pkg/storage/needle_read_write.go b/weed-fs/src/pkg/storage/needle_read_write.go
index 74b520fb8..62d267d24 100644
--- a/weed-fs/src/pkg/storage/needle_read_write.go
+++ b/weed-fs/src/pkg/storage/needle_read_write.go
@@ -8,20 +8,31 @@ import (
 	"pkg/util"
 )
 
-func (n *Needle) Append(w io.Writer, version Version) uint32 {
+const (
+	FlagGzip    = 0x01
+	FlagHasName = 0x02
+	FlagHasMime = 0x04
+)
+
+func (n *Needle) Append(w io.Writer, version Version) (size uint32, err error) {
 	switch version {
 	case Version1:
 		header := make([]byte, NeedleHeaderSize)
 		util.Uint32toBytes(header[0:4], n.Cookie)
 		util.Uint64toBytes(header[4:12], n.Id)
 		n.Size = uint32(len(n.Data))
+		size = n.Size
 		util.Uint32toBytes(header[12:16], n.Size)
-		w.Write(header)
-		w.Write(n.Data)
+		if _, err = w.Write(header); err != nil {
+			return
+		}
+		if _, err = w.Write(n.Data); err != nil {
+			return
+		}
 		padding := NeedlePaddingSize - ((NeedleHeaderSize + n.Size + NeedleChecksumSize) % NeedlePaddingSize)
 		util.Uint32toBytes(header[0:NeedleChecksumSize], n.Checksum.Value())
-		w.Write(header[0 : NeedleChecksumSize+padding])
-		return n.Size
+		_, err = w.Write(header[0 : NeedleChecksumSize+padding])
+		return
 	case Version2:
 		header := make([]byte, NeedleHeaderSize)
 		util.Uint32toBytes(header[0:4], n.Cookie)
@@ -36,52 +47,71 @@ func (n *Needle) Append(w io.Writer, version Version) uint32 {
 				n.Size = n.Size + 1 + uint32(n.MimeSize)
 			}
 		}
+		size = n.DataSize
 		util.Uint32toBytes(header[12:16], n.Size)
-		w.Write(header)
+		if _, err = w.Write(header); err != nil {
+			return
+		}
 		if n.DataSize > 0 {
 			util.Uint32toBytes(header[0:4], n.DataSize)
-			w.Write(header[0:4])
-			w.Write(n.Data)
+			if _, err = w.Write(header[0:4]); err != nil {
+				return
+			}
+			if _, err = w.Write(n.Data); err != nil {
+				return
+			}
 			util.Uint8toBytes(header[0:1], n.Flags)
-			w.Write(header[0:1])
+			if _, err = w.Write(header[0:1]); err != nil {
+				return
+			}
 		}
 		if n.HasName() {
 			util.Uint8toBytes(header[0:1], n.NameSize)
-			w.Write(header[0:1])
-			w.Write(n.Name)
+			if _, err = w.Write(header[0:1]); err != nil {
+				return
+			}
+			if _, err = w.Write(n.Name); err != nil {
+				return
+			}
 		}
 		if n.HasMime() {
 			util.Uint8toBytes(header[0:1], n.MimeSize)
-			w.Write(header[0:1])
-			w.Write(n.Mime)
+			if _, err = w.Write(header[0:1]); err != nil {
+				return
+			}
+			if _, err = w.Write(n.Mime); err != nil {
+				return
+			}
 		}
 		padding := NeedlePaddingSize - ((NeedleHeaderSize + n.Size + NeedleChecksumSize) % NeedlePaddingSize)
 		util.Uint32toBytes(header[0:NeedleChecksumSize], n.Checksum.Value())
-		w.Write(header[0 : NeedleChecksumSize+padding])
-		return n.DataSize
+		_, err = w.Write(header[0 : NeedleChecksumSize+padding])
+		return n.DataSize, err
 	}
-	return n.Size
+	return 0, fmt.Errorf("Unsupported Version! (%d)", version)
 }
-func (n *Needle) Read(r io.Reader, size uint32, version Version) (int, error) {
+
+func (n *Needle) Read(r io.Reader, size uint32, version Version) (ret int, err error) {
 	switch version {
 	case Version1:
 		bytes := make([]byte, NeedleHeaderSize+size+NeedleChecksumSize)
-		ret, e := r.Read(bytes)
+		if ret, err = r.Read(bytes); err != nil {
+			return
+		}
 		n.readNeedleHeader(bytes)
 		n.Data = bytes[NeedleHeaderSize : NeedleHeaderSize+size]
 		checksum := util.BytesToUint32(bytes[NeedleHeaderSize+size : NeedleHeaderSize+size+NeedleChecksumSize])
 		if checksum != NewCRC(n.Data).Value() {
 			return 0, errors.New("CRC error! Data On Disk Corrupted!")
 		}
-		return ret, e
+		return
 	case Version2:
 		if size == 0 {
 			return 0, nil
 		}
 		bytes := make([]byte, NeedleHeaderSize+size+NeedleChecksumSize)
-		ret, e := r.Read(bytes)
-		if e != nil {
-			return 0, e
+		if ret, err = r.Read(bytes); err != nil {
+			return
 		}
 		if ret != int(NeedleHeaderSize+size+NeedleChecksumSize) {
 			return 0, errors.New("File Entry Not Found!")
@@ -95,7 +125,7 @@ func (n *Needle) Read(r io.Reader, size uint32, version Version) (int, error) {
 		if checksum != NewCRC(n.Data).Value() {
 			return 0, errors.New("CRC error! Data On Disk Corrupted!")
 		}
-		return ret, e
+		return
 	}
 	return 0, fmt.Errorf("Unsupported Version! (%d)", version)
 }
@@ -126,13 +156,14 @@ func (n *Needle) readNeedleDataVersion2(bytes []byte) {
 		n.Mime = bytes[index : index+int(n.MimeSize)]
 	}
 }
-func ReadNeedleHeader(r *os.File, version Version) (n *Needle, bodyLength uint32) {
+func ReadNeedleHeader(r *os.File, version Version) (n *Needle, bodyLength uint32, err error) {
 	n = new(Needle)
 	if version == Version1 || version == Version2 {
 		bytes := make([]byte, NeedleHeaderSize)
-		count, e := r.Read(bytes)
-		if count <= 0 || e != nil {
-			return nil, 0
+		var count int
+		count, err = r.Read(bytes)
+		if count <= 0 || err != nil {
+			return nil, 0, err
 		}
 		n.readNeedleHeader(bytes)
 		padding := NeedlePaddingSize - ((n.Size + NeedleHeaderSize + NeedleChecksumSize) % NeedlePaddingSize)
@@ -143,37 +174,43 @@ func ReadNeedleHeader(r *os.File, version Version) (n *Needle, bodyLength uint32
 
 //n should be a needle already read the header
 //the input stream will read until next file entry
-func (n *Needle) ReadNeedleBody(r *os.File, version Version, bodyLength uint32) {
+func (n *Needle) ReadNeedleBody(r *os.File, version Version, bodyLength uint32) (err error) {
 	switch version {
 	case Version1:
 		bytes := make([]byte, bodyLength)
-		r.Read(bytes)
+		if _, err = r.Read(bytes); err != nil {
+			return
+		}
 		n.Data = bytes[:n.Size]
 		n.Checksum = NewCRC(n.Data)
 	case Version2:
 		bytes := make([]byte, bodyLength)
-		r.Read(bytes)
+		if _, err = r.Read(bytes); err != nil {
+			return
+		}
 		n.readNeedleDataVersion2(bytes[0:n.Size])
 		n.Checksum = NewCRC(n.Data)
+	default:
+		err = fmt.Errorf("Unsupported Version! (%d)", version)
 	}
 	return
 }
 
 func (n *Needle) IsGzipped() bool {
-	return n.Flags&0x01 == 0x01
+	return n.Flags&FlagGzip > 0
 }
 func (n *Needle) SetGzipped() {
-	n.Flags = n.Flags | 0x01
+	n.Flags = n.Flags | FlagGzip
 }
 func (n *Needle) HasName() bool {
-	return n.Flags&0x02 == 0x02
+	return n.Flags&FlagHasName > 0
 }
 func (n *Needle) SetHasName() {
-	n.Flags = n.Flags | 0x02
+	n.Flags = n.Flags | FlagHasName
 }
 func (n *Needle) HasMime() bool {
-	return n.Flags&0x04 == 0x04
+	return n.Flags&FlagHasMime > 0
 }
 func (n *Needle) SetHasMime() {
-	n.Flags = n.Flags | 0x04
+	n.Flags = n.Flags | FlagHasMime
 }
diff --git a/weed-fs/src/pkg/storage/store.go b/weed-fs/src/pkg/storage/store.go
index 79cf65e28..18af19aff 100644
--- a/weed-fs/src/pkg/storage/store.go
+++ b/weed-fs/src/pkg/storage/store.go
@@ -168,23 +168,23 @@ func (s *Store) Close() {
 		v.Close()
 	}
 }
-func (s *Store) Write(i VolumeId, n *Needle) uint32 {
+func (s *Store) Write(i VolumeId, n *Needle) (size uint32, err error) {
 	if v := s.volumes[i]; v != nil {
-		size := v.write(n)
-		if s.volumeSizeLimit < v.ContentSize()+uint64(size) && s.volumeSizeLimit >= v.ContentSize() {
+		size, err = v.write(n)
+		if err != nil && s.volumeSizeLimit < v.ContentSize()+uint64(size) && s.volumeSizeLimit >= v.ContentSize() {
 			log.Println("volume", i, "size is", v.ContentSize(), "close to", s.volumeSizeLimit)
 			s.Join()
 		}
-		return size
+		return
 	}
 	log.Println("volume", i, "not found!")
-	return 0
+	return
 }
-func (s *Store) Delete(i VolumeId, n *Needle) uint32 {
+func (s *Store) Delete(i VolumeId, n *Needle) (uint32, error) {
 	if v := s.volumes[i]; v != nil {
 		return v.delete(n)
 	}
-	return 0
+	return 0, nil
 }
 func (s *Store) Read(i VolumeId, n *Needle) (int, error) {
 	if v := s.volumes[i]; v != nil {
diff --git a/weed-fs/src/pkg/storage/volume.go b/weed-fs/src/pkg/storage/volume.go
index 6da991f60..933a84060 100644
--- a/weed-fs/src/pkg/storage/volume.go
+++ b/weed-fs/src/pkg/storage/volume.go
@@ -70,7 +70,11 @@ func (v *Volume) Close() {
 	v.dataFile.Close()
 }
 func (v *Volume) maybeWriteSuperBlock() {
-	stat, _ := v.dataFile.Stat()
+	stat, e := v.dataFile.Stat()
+	if e != nil {
+		fmt.Printf("failed to stat datafile %s: %s", v.dataFile, e)
+		return
+	}
 	if stat.Size() == 0 {
 		v.version = CurrentVersion
 		header := make([]byte, SuperBlockSize)
@@ -99,18 +103,23 @@ func (v *Volume) NeedToReplicate() bool {
 	return v.replicaType.GetCopyCount() > 1
 }
 
-func (v *Volume) write(n *Needle) uint32 {
+func (v *Volume) write(n *Needle) (size uint32, err error) {
 	v.accessLock.Lock()
 	defer v.accessLock.Unlock()
-	offset, _ := v.dataFile.Seek(0, 2)
-	ret := n.Append(v.dataFile, v.version)
+	var offset int64
+	if offset, err = v.dataFile.Seek(0, 2); err != nil {
+		return
+	}
+	if size, err = n.Append(v.dataFile, v.version); err != nil {
+		return
+	}
 	nv, ok := v.nm.Get(n.Id)
-	if !ok || int64(nv.Offset)*8 < offset {
-		v.nm.Put(n.Id, uint32(offset/8), n.Size)
+	if !ok || int64(nv.Offset)*NeedlePaddingSize < offset {
+		_, err = v.nm.Put(n.Id, uint32(offset/NeedlePaddingSize), n.Size)
 	}
-	return ret
+	return
 }
-func (v *Volume) delete(n *Needle) uint32 {
+func (v *Volume) delete(n *Needle) (uint32, error) {
 	v.accessLock.Lock()
 	defer v.accessLock.Unlock()
 	nv, ok := v.nm.Get(n.Id)
@@ -118,10 +127,10 @@ func (v *Volume) delete(n *Needle) uint32 {
 	if ok {
 		v.nm.Delete(n.Id)
 		v.dataFile.Seek(int64(nv.Offset*NeedlePaddingSize), 0)
-		n.Append(v.dataFile, v.version)
-		return nv.Size
+		_, err := n.Append(v.dataFile, v.version)
+		return nv.Size, err
 	}
-	return 0
+	return 0, nil
 }
 
 func (v *Volume) read(n *Needle) (int, error) {
@@ -164,33 +173,44 @@ func (v *Volume) commitCompact() error {
 }
 
 func (v *Volume) copyDataAndGenerateIndexFile(srcName, dstName, idxName string) (err error) {
-	src, err := os.OpenFile(srcName, os.O_RDONLY, 0644)
-	if err != nil {
-		return err
+	var (
+		src, dst, idx *os.File
+	)
+	if src, err = os.OpenFile(srcName, os.O_RDONLY, 0644); err != nil {
+		return
 	}
 	defer src.Close()
 
-	dst, err := os.OpenFile(dstName, os.O_WRONLY|os.O_CREATE, 0644)
-	if err != nil {
-		return err
+	if dst, err = os.OpenFile(dstName, os.O_WRONLY|os.O_CREATE, 0644); err != nil {
+		return
 	}
 	defer dst.Close()
 
-	idx, err := os.OpenFile(idxName, os.O_WRONLY|os.O_CREATE, 0644)
-	if err != nil {
-		return err
+	if idx, err = os.OpenFile(idxName, os.O_WRONLY|os.O_CREATE, 0644); err != nil {
+		return
 	}
 	defer idx.Close()
 
 	src.Seek(0, 0)
 	header := make([]byte, SuperBlockSize)
-	if _, error := src.Read(header); error == nil {
-		dst.Write(header)
+	if _, err = src.Read(header); err == nil {
+		_, err = dst.Write(header)
+	}
+	if err != nil {
+		return err
 	}
 
-	version, _, _ := ParseSuperBlock(header)
+	version, _, e := ParseSuperBlock(header)
+	if e != nil {
+		err = fmt.Errorf("cannot parse superblock: %s", e)
+		return
+	}
 
-	n, rest := ReadNeedleHeader(src, version)
+	n, rest, e := ReadNeedleHeader(src, version)
+	if e != nil {
+		err = fmt.Errorf("cannot read needle header: %s", e)
+		return
+	}
 	nm := NewNeedleMap(idx)
 	old_offset := uint32(SuperBlockSize)
 	new_offset := uint32(SuperBlockSize)
@@ -201,9 +221,15 @@ func (v *Volume) copyDataAndGenerateIndexFile(srcName, dstName, idxName string)
 			src.Seek(int64(rest), 1)
 		} else {
 			if nv.Size > 0 {
-				nm.Put(n.Id, new_offset/NeedlePaddingSize, n.Size)
-				n.ReadNeedleBody(src, version, rest)
-				n.Append(dst, v.version)
+				if _, err = nm.Put(n.Id, new_offset/NeedlePaddingSize, n.Size); err != nil {
+					return fmt.Errorf("cannot put needle: %s", err)
+				}
+				if err = n.ReadNeedleBody(src, version, rest); err != nil {
+					return fmt.Errorf("cannot read needle body: %s", err)
+				}
+				if _, err = n.Append(dst, v.version); err != nil {
+					return fmt.Errorf("cannot append needle: %s", err)
+				}
 				new_offset += rest + NeedleHeaderSize
 				//log.Println("saving key", n.Id, "volume offset", old_offset, "=>", new_offset, "data_size", n.Size, "rest", rest)
 			} else {
@@ -211,7 +237,9 @@ func (v *Volume) copyDataAndGenerateIndexFile(srcName, dstName, idxName string)
 			}
 		}
 		old_offset += rest + NeedleHeaderSize
-		n, rest = ReadNeedleHeader(src, version)
+		if n, rest, err = ReadNeedleHeader(src, version); err != nil {
+			return fmt.Errorf("cannot read needle header: %s", err)
+		}
 	}
 
 	return nil
diff --git a/weed-fs/src/pkg/topology/volume_layout.go b/weed-fs/src/pkg/topology/volume_layout.go
index 314aca69f..6d62128d9 100644
--- a/weed-fs/src/pkg/topology/volume_layout.go
+++ b/weed-fs/src/pkg/topology/volume_layout.go
@@ -38,8 +38,8 @@ func (vl *VolumeLayout) RegisterVolume(v *storage.VolumeInfo, dn *DataNode) {
 	}
 }
 
-func (vl *VolumeLayout) isWritable(v *storage.VolumeInfo) bool{
-    return uint64(v.Size) < vl.volumeSizeLimit && v.Version == storage.CurrentVersion
+func (vl *VolumeLayout) isWritable(v *storage.VolumeInfo) bool {
+	return uint64(v.Size) < vl.volumeSizeLimit && v.Version == storage.CurrentVersion
 }
 
 func (vl *VolumeLayout) Lookup(vid storage.VolumeId) []*DataNode {