Add "weed backup" command.

This is a pre-cursor for asynchronous replication.

go/operation/sync_volume.go

@@ -0,0 +1,54 @@
+package operation
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/url"
+
+	"github.com/chrislusf/seaweedfs/go/glog"
+	"github.com/chrislusf/seaweedfs/go/util"
+)
+
+type SyncVolumeResponse struct {
+	Replication     string `json:"Replication,omitempty"`
+	Ttl             string `json:"Ttl,omitempty"`
+	TailOffset      uint64 `json:"TailOffset,omitempty"`
+	CompactRevision uint16 `json:"CompactRevision,omitempty"`
+	IdxFileSize     uint64 `json:"IdxFileSize,omitempty"`
+	Error           string `json:"error,omitempty"`
+}
+
+func GetVolumeSyncStatus(server string, vid string) (*SyncVolumeResponse, error) {
+	values := make(url.Values)
+	values.Add("volume", vid)
+	jsonBlob, err := util.Post("http://"+server+"/admin/sync/status", values)
+	glog.V(2).Info("sync volume result :", string(jsonBlob))
+	if err != nil {
+		return nil, err
+	}
+	var ret SyncVolumeResponse
+	err = json.Unmarshal(jsonBlob, &ret)
+	if err != nil {
+		return nil, err
+	}
+	if ret.Error != "" {
+		return nil, fmt.Errorf("Volume %s get sync status error: %s", vid, ret.Error)
+	}
+	return &ret, nil
+}
+
+func GetVolumeIdxEntries(server string, vid string, eachEntryFn func(key uint64, offset, size uint32)) error {
+	values := make(url.Values)
+	values.Add("volume", vid)
+	line := make([]byte, 16)
+	err := util.GetBufferStream("http://"+server+"/admin/sync/index", values, line, func(bytes []byte) {
+		key := util.BytesToUint64(bytes[:8])
+		offset := util.BytesToUint32(bytes[8:12])
+		size := util.BytesToUint32(bytes[12:16])
+		eachEntryFn(key, offset, size)
+	})
+	if err != nil {
+		return err
+	}
+	return nil
+}

go/storage/needle_map.go

@@ -2,7 +2,9 @@ package storage
 
 import (
 	"fmt"
+	"io/ioutil"
 	"os"
+	"sync"
 
 	"github.com/chrislusf/seaweedfs/go/util"
 )
@@ -26,9 +28,60 @@ type NeedleMapper interface {
 	FileCount() int
 	DeletedCount() int
 	MaxFileKey() uint64
+	IndexFileSize() uint64
+	IndexFileContent() ([]byte, error)
+	IndexFileName() string
+}
+
+type baseNeedleMapper struct {
+	indexFile           *os.File
+	indexFileAccessLock sync.Mutex
+
+	mapMetric
+}
+
+func (nm baseNeedleMapper) IndexFileSize() uint64 {
+	stat, err := nm.indexFile.Stat()
+	if err == nil {
+		return uint64(stat.Size())
+	}
+	return 0
+}
+
+func (nm baseNeedleMapper) IndexFileName() string {
+	return nm.indexFile.Name()
+}
+
+func idxFileEntry(bytes []byte) (key uint64, offset uint32, size uint32) {
+	key = util.BytesToUint64(bytes[:8])
+	offset = util.BytesToUint32(bytes[8:12])
+	size = util.BytesToUint32(bytes[12:16])
+	return
+}
+func (nm baseNeedleMapper) appendToIndexFile(key uint64, offset uint32, size uint32) error {
+	bytes := make([]byte, 16)
+	util.Uint64toBytes(bytes[0:8], key)
+	util.Uint32toBytes(bytes[8:12], offset)
+	util.Uint32toBytes(bytes[12:16], 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)
+	}
+	_, err := nm.indexFile.Write(bytes)
+	return err
+}
+func (nm baseNeedleMapper) IndexFileContent() ([]byte, error) {
+	nm.indexFileAccessLock.Lock()
+	defer nm.indexFileAccessLock.Unlock()
+	return ioutil.ReadFile(nm.indexFile.Name())
 }
 
 type mapMetric struct {
+	indexFile *os.File
+
 	DeletionCounter     int    `json:"DeletionCounter"`
 	FileCounter         int    `json:"FileCounter"`
 	DeletionByteCounter uint64 `json:"DeletionByteCounter"`
@@ -36,20 +89,6 @@ type mapMetric struct {
 	MaximumFileKey      uint64 `json:"MaxFileKey"`
 }
 
-func appendToIndexFile(indexFile *os.File,
-	key uint64, offset uint32, size uint32) error {
-	bytes := make([]byte, 16)
-	util.Uint64toBytes(bytes[0:8], key)
-	util.Uint32toBytes(bytes[8:12], offset)
-	util.Uint32toBytes(bytes[12:16], size)
-	if _, err := indexFile.Seek(0, 2); err != nil {
-		return fmt.Errorf("cannot seek end of indexfile %s: %v",
-			indexFile.Name(), err)
-	}
-	_, err := indexFile.Write(bytes)
-	return err
-}
-
 func (mm *mapMetric) logDelete(deletedByteCount uint32) {
 	mm.DeletionByteCounter = mm.DeletionByteCounter + uint64(deletedByteCount)
 	mm.DeletionCounter++
@@ -66,3 +105,19 @@ func (mm *mapMetric) logPut(key uint64, oldSize uint32, newSize uint32) {
 		mm.DeletionByteCounter = mm.DeletionByteCounter + uint64(oldSize)
 	}
 }
+
+func (mm mapMetric) ContentSize() uint64 {
+	return mm.FileByteCounter
+}
+func (mm mapMetric) DeletedSize() uint64 {
+	return mm.DeletionByteCounter
+}
+func (mm mapMetric) FileCount() int {
+	return mm.FileCounter
+}
+func (mm mapMetric) DeletedCount() int {
+	return mm.DeletionCounter
+}
+func (mm mapMetric) MaxFileKey() uint64 {
+	return mm.MaximumFileKey
+}

go/storage/needle_map_boltdb.go

@@ -12,15 +12,15 @@ import (
 
 type BoltDbNeedleMap struct {
 	dbFileName string
-	indexFile  *os.File
 	db         *bolt.DB
-	mapMetric
+	baseNeedleMapper
 }
 
 var boltdbBucket = []byte("weed")
 
 func NewBoltDbNeedleMap(dbFileName string, indexFile *os.File) (m *BoltDbNeedleMap, err error) {
-	m = &BoltDbNeedleMap{indexFile: indexFile, dbFileName: dbFileName}
+	m = &BoltDbNeedleMap{dbFileName: dbFileName}
+	m.indexFile = indexFile
 	if !isBoltDbFresh(dbFileName, indexFile) {
 		glog.V(1).Infof("Start to Generate %s from %s", dbFileName, indexFile.Name())
 		generateBoltDbFile(dbFileName, indexFile)
@@ -101,7 +101,7 @@ func (m *BoltDbNeedleMap) Put(key uint64, offset uint32, size uint32) error {
 	}
 	m.logPut(key, oldSize, size)
 	// write to index file first
-	if err := appendToIndexFile(m.indexFile, key, offset, size); err != nil {
+	if err := m.appendToIndexFile(key, offset, size); err != nil {
 		return fmt.Errorf("cannot write to indexfile %s: %v", m.indexFile.Name(), err)
 	}
 	return boltDbWrite(m.db, key, offset, size)
@@ -148,7 +148,7 @@ func (m *BoltDbNeedleMap) Delete(key uint64) error {
 		m.logDelete(oldNeedle.Size)
 	}
 	// write to index file first
-	if err := appendToIndexFile(m.indexFile, key, 0, 0); err != nil {
+	if err := m.appendToIndexFile(key, 0, 0); err != nil {
 		return err
 	}
 	return boltDbDelete(m.db, key)
@@ -163,19 +163,3 @@ func (m *BoltDbNeedleMap) Destroy() error {
 	os.Remove(m.indexFile.Name())
 	return os.Remove(m.dbFileName)
 }
-
-func (m *BoltDbNeedleMap) ContentSize() uint64 {
-	return m.FileByteCounter
-}
-func (m *BoltDbNeedleMap) DeletedSize() uint64 {
-	return m.DeletionByteCounter
-}
-func (m *BoltDbNeedleMap) FileCount() int {
-	return m.FileCounter
-}
-func (m *BoltDbNeedleMap) DeletedCount() int {
-	return m.DeletionCounter
-}
-func (m *BoltDbNeedleMap) MaxFileKey() uint64 {
-	return m.MaximumFileKey
-}

go/storage/needle_map_leveldb.go

@@ -12,13 +12,13 @@ import (
 
 type LevelDbNeedleMap struct {
 	dbFileName string
-	indexFile  *os.File
 	db         *leveldb.DB
-	mapMetric
+	baseNeedleMapper
 }
 
 func NewLevelDbNeedleMap(dbFileName string, indexFile *os.File) (m *LevelDbNeedleMap, err error) {
-	m = &LevelDbNeedleMap{indexFile: indexFile, dbFileName: dbFileName}
+	m = &LevelDbNeedleMap{dbFileName: dbFileName}
+	m.indexFile = indexFile
 	if !isLevelDbFresh(dbFileName, indexFile) {
 		glog.V(1).Infof("Start to Generate %s from %s", dbFileName, indexFile.Name())
 		generateLevelDbFile(dbFileName, indexFile)
@@ -89,7 +89,7 @@ func (m *LevelDbNeedleMap) Put(key uint64, offset uint32, size uint32) error {
 	}
 	m.logPut(key, oldSize, size)
 	// write to index file first
-	if err := appendToIndexFile(m.indexFile, key, offset, size); err != nil {
+	if err := m.appendToIndexFile(key, offset, size); err != nil {
 		return fmt.Errorf("cannot write to indexfile %s: %v", m.indexFile.Name(), err)
 	}
 	return levelDbWrite(m.db, key, offset, size)
@@ -117,7 +117,7 @@ func (m *LevelDbNeedleMap) Delete(key uint64) error {
 		m.logDelete(oldNeedle.Size)
 	}
 	// write to index file first
-	if err := appendToIndexFile(m.indexFile, key, 0, 0); err != nil {
+	if err := m.appendToIndexFile(key, 0, 0); err != nil {
 		return err
 	}
 	return levelDbDelete(m.db, key)
@@ -132,19 +132,3 @@ func (m *LevelDbNeedleMap) Destroy() error {
 	os.Remove(m.indexFile.Name())
 	return os.Remove(m.dbFileName)
 }
-
-func (m *LevelDbNeedleMap) ContentSize() uint64 {
-	return m.FileByteCounter
-}
-func (m *LevelDbNeedleMap) DeletedSize() uint64 {
-	return m.DeletionByteCounter
-}
-func (m *LevelDbNeedleMap) FileCount() int {
-	return m.FileCounter
-}
-func (m *LevelDbNeedleMap) DeletedCount() int {
-	return m.DeletionCounter
-}
-func (m *LevelDbNeedleMap) MaxFileKey() uint64 {
-	return m.MaximumFileKey
-}

go/storage/needle_map_memory.go

@@ -5,21 +5,19 @@ import (
 	"os"
 
 	"github.com/chrislusf/seaweedfs/go/glog"
-	"github.com/chrislusf/seaweedfs/go/util"
 )
 
 type NeedleMap struct {
-	indexFile *os.File
 	m CompactMap
 
-	mapMetric
+	baseNeedleMapper
 }
 
 func NewNeedleMap(file *os.File) *NeedleMap {
 	nm := &NeedleMap{
 		m: NewCompactMap(),
-		indexFile: file,
 	}
+	nm.indexFile = file
 	return nm
 }
 
@@ -70,9 +68,7 @@ func WalkIndexFile(r *os.File, fn func(key uint64, offset, size uint32) error) e
 
 	for count > 0 && e == nil || e == io.EOF {
 		for i = 0; i+16 <= count; i += 16 {
-			key = util.BytesToUint64(bytes[i : i+8])
+			key, offset, size = idxFileEntry(bytes[i : i+16])
-			offset = util.BytesToUint32(bytes[i+8 : i+12])
-			size = util.BytesToUint32(bytes[i+12 : i+16])
 			if e = fn(key, offset, size); e != nil {
 				return e
 			}
@@ -90,7 +86,7 @@ func WalkIndexFile(r *os.File, fn func(key uint64, offset, size uint32) error) e
 func (nm *NeedleMap) Put(key uint64, offset uint32, size uint32) error {
 	oldSize := nm.m.Set(Key(key), offset, size)
 	nm.logPut(key, oldSize, size)
-	return appendToIndexFile(nm.indexFile, key, offset, size)
+	return nm.appendToIndexFile(key, offset, size)
 }
 func (nm *NeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
 	element, ok = nm.m.Get(Key(key))
@@ -99,7 +95,7 @@ func (nm *NeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
 func (nm *NeedleMap) Delete(key uint64) error {
 	deletedBytes := nm.m.Delete(Key(key))
 	nm.logDelete(deletedBytes)
-	return appendToIndexFile(nm.indexFile, key, 0, 0)
+	return nm.appendToIndexFile(key, 0, 0)
 }
 func (nm *NeedleMap) Close() {
 	_ = nm.indexFile.Close()
@@ -108,19 +104,3 @@ func (nm *NeedleMap) Destroy() error {
 	nm.Close()
 	return os.Remove(nm.indexFile.Name())
 }
-func (nm NeedleMap) ContentSize() uint64 {
-	return nm.FileByteCounter
-}
-func (nm NeedleMap) DeletedSize() uint64 {
-	return nm.DeletionByteCounter
-}
-func (nm NeedleMap) FileCount() int {
-	return nm.FileCounter
-}
-func (nm NeedleMap) DeletedCount() int {
-	return nm.DeletionCounter
-}
-
-func (nm NeedleMap) MaxFileKey() uint64 {
-	return nm.MaximumFileKey
-}

go/storage/needle_read_write.go

@@ -135,49 +135,37 @@ func (n *Needle) Append(w io.Writer, version Version) (size uint32, err error) {
 	return 0, fmt.Errorf("Unsupported Version! (%d)", version)
 }
 
-func (n *Needle) Read(r *os.File, offset int64, size uint32, version Version) (ret int, err error) {
+func ReadNeedleBlob(r *os.File, offset int64, size uint32) (bytes []byte, err error) {
+	padding := NeedlePaddingSize - ((NeedleHeaderSize + size + NeedleChecksumSize) % NeedlePaddingSize)
+	bytes = make([]byte, NeedleHeaderSize+size+NeedleChecksumSize+padding)
+	_, err = r.ReadAt(bytes, offset)
+	return
+}
+
+func (n *Needle) ReadData(r *os.File, offset int64, size uint32, version Version) (err error) {
+	bytes, err := ReadNeedleBlob(r, offset, size)
+	if err != nil {
+		return err
+	}
+	n.ParseNeedleHeader(bytes)
+	if n.Size != size {
+		return fmt.Errorf("File Entry Not Found. Needle %d Memory %d", n.Size, size)
+	}
 	switch version {
 	case Version1:
-		bytes := make([]byte, NeedleHeaderSize+size+NeedleChecksumSize)
-		if ret, err = r.ReadAt(bytes, offset); err != nil {
-			return
-		}
-		n.readNeedleHeader(bytes)
 		n.Data = bytes[NeedleHeaderSize : NeedleHeaderSize+size]
+	case Version2:
+		n.readNeedleDataVersion2(bytes[NeedleHeaderSize : NeedleHeaderSize+int(n.Size)])
+	}
 	checksum := util.BytesToUint32(bytes[NeedleHeaderSize+size : NeedleHeaderSize+size+NeedleChecksumSize])
 	newChecksum := NewCRC(n.Data)
 	if checksum != newChecksum.Value() {
-			return 0, errors.New("CRC error! Data On Disk Corrupted")
+		return errors.New("CRC error! Data On Disk Corrupted")
 	}
 	n.Checksum = newChecksum
-		return
+	return nil
-	case Version2:
-		if size == 0 {
-			return 0, nil
-		}
-		bytes := make([]byte, NeedleHeaderSize+size+NeedleChecksumSize)
-		if ret, err = r.ReadAt(bytes, offset); err != nil {
-			return
-		}
-		if ret != int(NeedleHeaderSize+size+NeedleChecksumSize) {
-			return 0, errors.New("File Entry Not Found")
-		}
-		n.readNeedleHeader(bytes)
-		if n.Size != size {
-			return 0, fmt.Errorf("File Entry Not Found. Needle %d Memory %d", n.Size, size)
-		}
-		n.readNeedleDataVersion2(bytes[NeedleHeaderSize : NeedleHeaderSize+int(n.Size)])
-		checksum := util.BytesToUint32(bytes[NeedleHeaderSize+n.Size : NeedleHeaderSize+n.Size+NeedleChecksumSize])
-		newChecksum := NewCRC(n.Data)
-		if checksum != newChecksum.Value() {
-			return 0, errors.New("CRC Found Data On Disk Corrupted")
-		}
-		n.Checksum = newChecksum
-		return
-	}
-	return 0, fmt.Errorf("Unsupported Version! (%d)", version)
 }
-func (n *Needle) readNeedleHeader(bytes []byte) {
+func (n *Needle) ParseNeedleHeader(bytes []byte) {
 	n.Cookie = util.BytesToUint32(bytes[0:4])
 	n.Id = util.BytesToUint64(bytes[4:12])
 	n.Size = util.BytesToUint32(bytes[12:NeedleHeaderSize])
@@ -228,7 +216,7 @@ func ReadNeedleHeader(r *os.File, version Version, offset int64) (n *Needle, bod
 		if count <= 0 || err != nil {
 			return nil, 0, err
 		}
-		n.readNeedleHeader(bytes)
+		n.ParseNeedleHeader(bytes)
 		padding := NeedlePaddingSize - ((n.Size + NeedleHeaderSize + NeedleChecksumSize) % NeedlePaddingSize)
 		bodyLength = n.Size + NeedleChecksumSize + padding
 	}

go/storage/store.go

@@ -371,9 +371,9 @@ func (s *Store) Delete(i VolumeId, n *Needle) (uint32, error) {
 	}
 	return 0, nil
 }
-func (s *Store) Read(i VolumeId, n *Needle) (int, error) {
+func (s *Store) ReadVolumeNeedle(i VolumeId, n *Needle) (int, error) {
 	if v := s.findVolume(i); v != nil {
-		return v.read(n)
+		return v.readNeedle(n)
 	}
 	return 0, fmt.Errorf("Volume %v not found!", i)
 }

go/storage/volume.go

@@ -54,6 +54,9 @@ func (v *Volume) FileName() (fileName string) {
 	}
 	return
 }
+func (v *Volume) DataFile() *os.File {
+	return v.dataFile
+}
 func (v *Volume) load(alsoLoadIndex bool, createDatIfMissing bool, needleMapKind NeedleMapType) error {
 	var e error
 	fileName := v.FileName()
@@ -152,7 +155,7 @@ func (v *Volume) isFileUnchanged(n *Needle) bool {
 	nv, ok := v.nm.Get(n.Id)
 	if ok && nv.Offset > 0 {
 		oldNeedle := new(Needle)
-		_, err := oldNeedle.Read(v.dataFile, int64(nv.Offset)*NeedlePaddingSize, nv.Size, v.Version())
+		err := oldNeedle.ReadData(v.dataFile, int64(nv.Offset)*NeedlePaddingSize, nv.Size, v.Version())
 		if err != nil {
 			glog.V(0).Infof("Failed to check updated file %v", err)
 			return false
@@ -180,6 +183,30 @@ func (v *Volume) Destroy() (err error) {
 	return
 }
 
+// AppendBlob append a blob to end of the data file, used in replication
+func (v *Volume) AppendBlob(b []byte) (offset int64, err error) {
+	if v.readOnly {
+		err = fmt.Errorf("%s is read-only", v.dataFile.Name())
+		return
+	}
+	v.dataFileAccessLock.Lock()
+	defer v.dataFileAccessLock.Unlock()
+	if offset, err = v.dataFile.Seek(0, 2); err != nil {
+		glog.V(0).Infof("failed to seek the end of file: %v", err)
+		return
+	}
+	//ensure file writing starting from aligned positions
+	if offset%NeedlePaddingSize != 0 {
+		offset = offset + (NeedlePaddingSize - offset%NeedlePaddingSize)
+		if offset, err = v.dataFile.Seek(offset, 0); err != nil {
+			glog.V(0).Infof("failed to align in datafile %s: %v", v.dataFile.Name(), err)
+			return
+		}
+	}
+	v.dataFile.Write(b)
+	return
+}
+
 func (v *Volume) write(n *Needle) (size uint32, err error) {
 	glog.V(4).Infof("writing needle %s", NewFileIdFromNeedle(v.Id, n).String())
 	if v.readOnly {
@@ -250,17 +277,19 @@ func (v *Volume) delete(n *Needle) (uint32, error) {
 	return 0, nil
 }
 
-func (v *Volume) read(n *Needle) (int, error) {
+// read fills in Needle content by looking up n.Id from NeedleMapper
+func (v *Volume) readNeedle(n *Needle) (int, error) {
 	nv, ok := v.nm.Get(n.Id)
 	if !ok || nv.Offset == 0 {
 		return -1, errors.New("Not Found")
 	}
-	bytesRead, err := n.Read(v.dataFile, int64(nv.Offset)*NeedlePaddingSize, nv.Size, v.Version())
+	err := n.ReadData(v.dataFile, int64(nv.Offset)*NeedlePaddingSize, nv.Size, v.Version())
 	if err != nil {
-		return bytesRead, err
+		return 0, err
 	}
+	bytesRead := len(n.Data)
 	if !n.HasTtl() {
-		return bytesRead, err
+		return bytesRead, nil
 	}
 	ttlMinutes := n.Ttl.Minutes()
 	if ttlMinutes == 0 {

go/storage/volume_sync.go

@@ -0,0 +1,213 @@
+package storage
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/url"
+	"os"
+	"sort"
+	"strconv"
+
+	"github.com/chrislusf/seaweedfs/go/glog"
+	"github.com/chrislusf/seaweedfs/go/operation"
+	"github.com/chrislusf/seaweedfs/go/util"
+)
+
+// The volume sync with a master volume via 2 steps:
+// 1. The slave checks master side to find subscription checkpoint
+//	  to setup the replication.
+// 2. The slave receives the updates from master
+
+/*
+Assume the slave volume needs to follow the master volume.
+
+The master volume could be compacted, and could be many files ahead of
+slave volume.
+
+Step 1:
+The slave volume will ask the master volume for a snapshot
+of (existing file entries, last offset, number of compacted times).
+
+For each entry x in master existing file entries:
+  if x does not exist locally:
+    add x locally
+
+For each entry y in local slave existing file entries:
+  if y does not exist on master:
+    delete y locally
+
+Step 2:
+After this, use the last offset and number of compacted times to request
+the master volume to send a new file, and keep looping. If the number of
+compacted times is changed, go back to step 1 (very likely this can be
+optimized more later).
+
+*/
+
+func (v *Volume) Synchronize(volumeServer string) (err error) {
+	var lastCompactRevision uint16 = 0
+	var compactRevision uint16 = 0
+	var masterMap CompactMap
+	for i := 0; i < 3; i++ {
+		if masterMap, _, compactRevision, err = fetchVolumeFileEntries(volumeServer, v.Id); err != nil {
+			return fmt.Errorf("Failed to sync volume %d entries with %s: %v", v.Id, volumeServer, err)
+		}
+		if lastCompactRevision != compactRevision && lastCompactRevision != 0 {
+			if err = v.Compact(); err != nil {
+				return fmt.Errorf("Compact Volume before synchronizing %v", err)
+			}
+			if err = v.commitCompact(); err != nil {
+				return fmt.Errorf("Commit Compact before synchronizing %v", err)
+			}
+		}
+		lastCompactRevision = compactRevision
+		if err = v.trySynchronizing(volumeServer, masterMap, compactRevision); err == nil {
+			return
+		}
+	}
+	return
+}
+
+type ByOffset []NeedleValue
+
+func (a ByOffset) Len() int           { return len(a) }
+func (a ByOffset) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a ByOffset) Less(i, j int) bool { return a[i].Offset < a[j].Offset }
+
+// trySynchronizing sync with remote volume server incrementally by
+// make up the local and remote delta.
+func (v *Volume) trySynchronizing(volumeServer string, masterMap CompactMap, compactRevision uint16) error {
+	slaveIdxFile, err := os.Open(v.nm.IndexFileName())
+	if err != nil {
+		return fmt.Errorf("Open volume %d index file: %v", v.Id, err)
+	}
+	defer slaveIdxFile.Close()
+	slaveMap, err := LoadNeedleMap(slaveIdxFile)
+	if err != nil {
+		return fmt.Errorf("Load volume %d index file: %v", v.Id, err)
+	}
+	var delta []NeedleValue
+	if err := masterMap.Visit(func(needleValue NeedleValue) error {
+		if needleValue.Key == 0 {
+			return nil
+		}
+		if _, ok := slaveMap.Get(uint64(needleValue.Key)); ok {
+			return nil // skip intersection
+		}
+		delta = append(delta, needleValue)
+		return nil
+	}); err != nil {
+		return fmt.Errorf("Add master entry: %v", err)
+	}
+	if err := slaveMap.m.Visit(func(needleValue NeedleValue) error {
+		if needleValue.Key == 0 {
+			return nil
+		}
+		if _, ok := masterMap.Get(needleValue.Key); ok {
+			return nil // skip intersection
+		}
+		needleValue.Size = 0
+		delta = append(delta, needleValue)
+		return nil
+	}); err != nil {
+		return fmt.Errorf("Remove local entry: %v", err)
+	}
+
+	// simulate to same ordering of remote .dat file needle entries
+	sort.Sort(ByOffset(delta))
+
+	// make up the delta
+	fetchCount := 0
+	volumeDataContentHandlerUrl := "http://" + volumeServer + "/admin/sync/data"
+	for _, needleValue := range delta {
+		if needleValue.Size == 0 {
+			// remove file entry from local
+			v.removeNeedle(needleValue.Key)
+			continue
+		}
+		// add master file entry to local data file
+		if err := v.fetchNeedle(volumeDataContentHandlerUrl, needleValue, compactRevision); err != nil {
+			glog.V(0).Infof("Fetch needle %v from %s: %v", needleValue, volumeServer, err)
+			return err
+		}
+		fetchCount++
+	}
+	glog.V(1).Infof("Fetched %d needles from %s", fetchCount, volumeServer)
+	return nil
+}
+
+func fetchVolumeFileEntries(volumeServer string, vid VolumeId) (m CompactMap, lastOffset uint64, compactRevision uint16, err error) {
+	m = NewCompactMap()
+
+	syncStatus, err := operation.GetVolumeSyncStatus(volumeServer, vid.String())
+	if err != nil {
+		return m, 0, 0, err
+	}
+
+	total := 0
+	err = operation.GetVolumeIdxEntries(volumeServer, vid.String(), func(key uint64, offset, size uint32) {
+		// println("remote key", key, "offset", offset*NeedlePaddingSize, "size", size)
+		if offset != 0 && size != 0 {
+			m.Set(Key(key), offset, size)
+		} else {
+			m.Delete(Key(key))
+		}
+		total++
+	})
+
+	glog.V(2).Infof("server %s volume %d, entries %d, last offset %d, revision %d", volumeServer, vid, total, syncStatus.TailOffset, syncStatus.CompactRevision)
+	return m, syncStatus.TailOffset, syncStatus.CompactRevision, err
+
+}
+
+func (v *Volume) GetVolumeSyncStatus() operation.SyncVolumeResponse {
+	var syncStatus = operation.SyncVolumeResponse{}
+	if stat, err := v.dataFile.Stat(); err == nil {
+		syncStatus.TailOffset = uint64(stat.Size())
+	}
+	syncStatus.IdxFileSize = v.nm.IndexFileSize()
+	syncStatus.CompactRevision = v.SuperBlock.CompactRevision
+	syncStatus.Ttl = v.SuperBlock.Ttl.String()
+	syncStatus.Replication = v.SuperBlock.ReplicaPlacement.String()
+	return syncStatus
+}
+
+func (v *Volume) IndexFileContent() ([]byte, error) {
+	return v.nm.IndexFileContent()
+}
+
+// removeNeedle removes one needle by needle key
+func (v *Volume) removeNeedle(key Key) {
+	n := new(Needle)
+	n.Id = uint64(key)
+	v.delete(n)
+}
+
+// fetchNeedle fetches a remote volume needle by vid, id, offset
+// The compact revision is checked first in case the remote volume
+// is compacted and the offset is invalid any more.
+func (v *Volume) fetchNeedle(volumeDataContentHandlerUrl string,
+	needleValue NeedleValue, compactRevision uint16) error {
+	// add master file entry to local data file
+	values := make(url.Values)
+	values.Add("revision", strconv.Itoa(int(compactRevision)))
+	values.Add("volume", v.Id.String())
+	values.Add("id", needleValue.Key.String())
+	values.Add("offset", strconv.FormatUint(uint64(needleValue.Offset), 10))
+	values.Add("size", strconv.FormatUint(uint64(needleValue.Size), 10))
+	glog.V(4).Infof("Fetch %+v", needleValue)
+	return util.GetUrlStream(volumeDataContentHandlerUrl, values, func(r io.Reader) error {
+		b, err := ioutil.ReadAll(r)
+		if err != nil {
+			return fmt.Errorf("Reading from %s error: %v", volumeDataContentHandlerUrl, err)
+		}
+		offset, err := v.AppendBlob(b)
+		if err != nil {
+			return fmt.Errorf("Appending volume %d error: %v", v.Id, err)
+		}
+		// println("add key", needleValue.Key, "offset", offset, "size", needleValue.Size)
+		v.nm.Put(uint64(needleValue.Key), uint32(offset/NeedlePaddingSize), needleValue.Size)
+		return nil
+	})
+}

go/util/http_util.go

@@ -3,6 +3,7 @@ package util
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"net/http"
 	"net/url"
@@ -84,6 +85,43 @@ func Delete(url string, jwt security.EncodedJwt) error {
 	return nil
 }
 
+func GetBufferStream(url string, values url.Values, allocatedBytes []byte, eachBuffer func([]byte)) error {
+	r, err := client.PostForm(url, values)
+	if err != nil {
+		return err
+	}
+	defer r.Body.Close()
+	if r.StatusCode != 200 {
+		return fmt.Errorf("%s: %s", url, r.Status)
+	}
+	bufferSize := len(allocatedBytes)
+	for {
+		n, err := r.Body.Read(allocatedBytes)
+		if n == bufferSize {
+			eachBuffer(allocatedBytes)
+		}
+		if err != nil {
+			if err == io.EOF {
+				return nil
+			}
+			return err
+		}
+	}
+	return nil
+}
+
+func GetUrlStream(url string, values url.Values, readFn func(io.Reader) error) error {
+	r, err := client.PostForm(url, values)
+	if err != nil {
+		return err
+	}
+	defer r.Body.Close()
+	if r.StatusCode != 200 {
+		return fmt.Errorf("%s: %s", url, r.Status)
+	}
+	return readFn(r.Body)
+}
+
 func DownloadUrl(fileUrl string) (filename string, content []byte, e error) {
 	response, err := client.Get(fileUrl)
 	if err != nil {

go/weed/backup.go

@@ -0,0 +1,90 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/chrislusf/seaweedfs/go/operation"
+	"github.com/chrislusf/seaweedfs/go/storage"
+)
+
+var (
+	s BackupOptions
+)
+
+type BackupOptions struct {
+	master     *string
+	collection *string
+	dir        *string
+	volumeId   *int
+}
+
+func init() {
+	cmdBackup.Run = runBackup // break init cycle
+	s.master = cmdBackup.Flag.String("server", "localhost:9333", "SeaweedFS master location")
+	s.collection = cmdBackup.Flag.String("collection", "", "collection name")
+	s.dir = cmdBackup.Flag.String("dir", ".", "directory to store volume data files")
+	s.volumeId = cmdBackup.Flag.Int("volumeId", -1, "a volume id. The volume .dat and .idx files should already exist in the dir.")
+}
+
+var cmdBackup = &Command{
+	UsageLine: "backup -dir=. -volumeId=234 -server=localhost:9333",
+	Short:     "incrementally backup a volume to local folder",
+	Long: `Incrementally backup volume data.
+	
+	It is expected that you use this inside a script, to loop through
+	all possible volume ids that needs to be backup to local folder.
+	
+	The volume id does not need to exist locally or even remotely.
+	This will help to backup future new volumes.
+	
+	Usually backing up is just copying the .dat (and .idx) files.
+	But it's tricky to incremententally copy the differences.
+	
+	The complexity comes when there are multiple addition, deletion and compaction.
+	This tool will handle them correctly and efficiently, avoiding unnecessary data transporation.
+  `,
+}
+
+func runBackup(cmd *Command, args []string) bool {
+	if *s.volumeId == -1 {
+		return false
+	}
+	vid := storage.VolumeId(*s.volumeId)
+
+	// find volume location, replication, ttl info
+	lookup, err := operation.Lookup(*s.master, vid.String())
+	if err != nil {
+		fmt.Printf("Error looking up volume %d: %v\n", vid, err)
+		return true
+	}
+	volumeServer := lookup.Locations[0].Url
+
+	stats, err := operation.GetVolumeSyncStatus(volumeServer, vid.String())
+	if err != nil {
+		fmt.Printf("Error get volume %d status: %v\n", vid, err)
+		return true
+	}
+	ttl, err := storage.ReadTTL(stats.Ttl)
+	if err != nil {
+		fmt.Printf("Error get volume %d ttl %s: %v\n", vid, stats.Ttl, err)
+		return true
+	}
+	replication, err := storage.NewReplicaPlacementFromString(stats.Replication)
+	if err != nil {
+		fmt.Printf("Error get volume %d replication %s : %v\n", vid, stats.Replication, err)
+		return true
+	}
+
+	v, err := storage.NewVolume(*s.dir, *s.collection, vid, storage.NeedleMapInMemory, replication, ttl)
+	if err != nil {
+		fmt.Printf("Error creating or reading from volume %d: %v\n", vid, err)
+		return true
+	}
+
+	if err := v.Synchronize(volumeServer); err != nil {
+		fmt.Printf("Error synchronizing volume %d: %v\n", vid, err)
+		return true
+	}
+
+	return true
+}

go/weed/compact.go

@@ -7,7 +7,6 @@ import (
 
 func init() {
 	cmdCompact.Run = runCompact // break init cycle
-	cmdCompact.IsDebug = cmdCompact.Flag.Bool("debug", false, "enable debug mode")
 }
 
 var cmdCompact = &Command{

go/weed/weed.go

@@ -21,6 +21,7 @@ var server *string
 
 var commands = []*Command{
 	cmdBenchmark,
+	cmdBackup,
 	cmdCompact,
 	cmdFix,
 	cmdServer,

go/weed/weed_server/volume_server.go

@@ -51,6 +51,9 @@ func NewVolumeServer(adminMux, publicMux *http.ServeMux, ip string,
 	adminMux.HandleFunc("/admin/vacuum/compact", vs.guard.WhiteList(vs.vacuumVolumeCompactHandler))
 	adminMux.HandleFunc("/admin/vacuum/commit", vs.guard.WhiteList(vs.vacuumVolumeCommitHandler))
 	adminMux.HandleFunc("/admin/delete_collection", vs.guard.WhiteList(vs.deleteCollectionHandler))
+	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("/stats/counter", vs.guard.WhiteList(statsCounterHandler))
 	adminMux.HandleFunc("/stats/memory", vs.guard.WhiteList(statsMemoryHandler))
 	adminMux.HandleFunc("/stats/disk", vs.guard.WhiteList(vs.statsDiskHandler))

go/weed/weed_server/volume_server_handlers_read.go

@@ -47,7 +47,7 @@ func (vs *VolumeServer) GetOrHeadHandler(w http.ResponseWriter, r *http.Request)
 		return
 	}
 	cookie := n.Cookie
-	count, e := vs.store.Read(volumeId, n)
+	count, e := vs.store.ReadVolumeNeedle(volumeId, n)
 	glog.V(4).Infoln("read bytes", count, "error", e)
 	if e != nil || count <= 0 {
 		glog.V(0).Infoln("read error:", e, r.URL.Path)

go/weed/weed_server/volume_server_handlers_sync.go

@@ -0,0 +1,86 @@
+package weed_server
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/chrislusf/seaweedfs/go/glog"
+	"github.com/chrislusf/seaweedfs/go/storage"
+	"github.com/chrislusf/seaweedfs/go/util"
+)
+
+func (vs *VolumeServer) getVolumeSyncStatusHandler(w http.ResponseWriter, r *http.Request) {
+	v, err := vs.getVolume("volume", r)
+	if v == nil {
+		writeJsonError(w, r, http.StatusBadRequest, err)
+		return
+	}
+	syncStat := v.GetVolumeSyncStatus()
+	if syncStat.Error != "" {
+		writeJsonError(w, r, http.StatusInternalServerError, fmt.Errorf("Get Volume %d status error: %s", v.Id, syncStat.Error))
+		glog.V(2).Infoln("getVolumeSyncStatusHandler volume =", r.FormValue("volume"), ", error =", err)
+	} else {
+		writeJsonQuiet(w, r, http.StatusOK, syncStat)
+	}
+}
+
+func (vs *VolumeServer) getVolumeIndexContentHandler(w http.ResponseWriter, r *http.Request) {
+	v, err := vs.getVolume("volume", r)
+	if v == nil {
+		writeJsonError(w, r, http.StatusBadRequest, err)
+		return
+	}
+	content, err := v.IndexFileContent()
+	if err != nil {
+		writeJsonError(w, r, http.StatusInternalServerError, err)
+		return
+	}
+	w.Write(content)
+}
+
+func (vs *VolumeServer) getVolumeDataContentHandler(w http.ResponseWriter, r *http.Request) {
+	v, err := vs.getVolume("volume", r)
+	if v == nil {
+		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("Not Found volume: %v", err))
+		return
+	}
+	if int(v.SuperBlock.CompactRevision) != util.ParseInt(r.FormValue("revision"), 0) {
+		writeJsonError(w, r, http.StatusExpectationFailed, fmt.Errorf("Requested Volume Revision is %s, but current revision is %d", r.FormValue("revision"), v.SuperBlock.CompactRevision))
+		return
+	}
+	offset := uint32(util.ParseUint64(r.FormValue("offset"), 0))
+	size := uint32(util.ParseUint64(r.FormValue("size"), 0))
+	content, err := storage.ReadNeedleBlob(v.DataFile(), int64(offset)*storage.NeedlePaddingSize, size)
+	if err != nil {
+		writeJsonError(w, r, http.StatusInternalServerError, err)
+		return
+	}
+
+	id := util.ParseUint64(r.FormValue("id"), 0)
+	n := new(storage.Needle)
+	n.ParseNeedleHeader(content)
+	if id != n.Id {
+		writeJsonError(w, r, http.StatusNotFound, fmt.Errorf("Expected file entry id %d, but found %d", id, n.Id))
+		return
+	}
+
+	w.Write(content)
+}
+
+func (vs *VolumeServer) getVolume(volumeParameterName string, r *http.Request) (*storage.Volume, error) {
+	volumeIdString := r.FormValue(volumeParameterName)
+	if volumeIdString == "" {
+		err := fmt.Errorf("Empty Volume Id: Need to pass in %s=the_volume_id.", volumeParameterName)
+		return nil, err
+	}
+	vid, err := storage.NewVolumeId(volumeIdString)
+	if err != nil {
+		err = fmt.Errorf("Volume Id %s is not a valid unsigned integer", volumeIdString)
+		return nil, err
+	}
+	v := vs.store.GetVolume(vid)
+	if v == nil {
+		return nil, fmt.Errorf("Not Found Volume Id %s: %d", volumeIdString, vid)
+	}
+	return v, nil
+}

go/weed/weed_server/volume_server_handlers_write.go

@@ -53,7 +53,7 @@ func (vs *VolumeServer) DeleteHandler(w http.ResponseWriter, r *http.Request) {
 	glog.V(2).Infoln("deleting", n)
 
 	cookie := n.Cookie
-	count, ok := vs.store.Read(volumeId, n)
+	count, ok := vs.store.ReadVolumeNeedle(volumeId, n)
 
 	if ok != nil {
 		m := make(map[string]uint32)
@@ -94,7 +94,7 @@ func (vs *VolumeServer) batchDeleteHandler(w http.ResponseWriter, r *http.Reques
 		n.ParsePath(id_cookie)
 		glog.V(4).Infoln("batch deleting", n)
 		cookie := n.Cookie
-		if _, err := vs.store.Read(volumeId, n); err != nil {
+		if _, err := vs.store.ReadVolumeNeedle(volumeId, n); err != nil {
 			ret = append(ret, operation.DeleteResult{Fid: fid, Error: err.Error()})
 			continue
 		}