diff --git a/weed/storage/backend/disk_file.go b/weed/storage/backend/disk_file.go
index 2b04c8df2..aee02e7be 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/util/buffered_writer"
 	"os"
 	"time"
 )
@@ -12,32 +14,64 @@ var (
 type DiskFile struct {
 	File         *os.File
 	fullFilePath string
+	bufWriterAt  *buffered_writer.TimedWriteBuffer
+	fileSize     int64
+	modTime      time.Time
 }
 
 func NewDiskFile(f *os.File) *DiskFile {
+	stat, e := f.Stat()
+	if e != nil {
+		glog.Fatalf("stat file %s: %v", f.Name(), e)
+	}
+
 	return &DiskFile{
 		fullFilePath: f.Name(),
 		File:         f,
+		bufWriterAt:  buffered_writer.NewTimedWriteBuffer(f, 1*1024*1024, 200*time.Millisecond, stat.Size()),
+		fileSize:     stat.Size(),
+		modTime:      stat.ModTime(),
 	}
 }
 
 func (df *DiskFile) ReadAt(p []byte, off int64) (n int, err error) {
+	n, _ = df.bufWriterAt.ReadAt(p, off)
+	if len(p) == n {
+		return
+	}
 	return df.File.ReadAt(p, off)
 }
 
 func (df *DiskFile) WriteAt(p []byte, off int64) (n int, err error) {
-	return df.File.WriteAt(p, off)
+	n, err = df.bufWriterAt.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) 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 {
+	df.bufWriterAt.Close()
 	return df.File.Close()
 }
 
 func (df *DiskFile) GetStat() (datSize int64, modTime time.Time, err error) {
+	if df.fileSize != 0 {
+		return df.fileSize, df.modTime, nil
+	}
 	stat, e := df.File.Stat()
 	if e == nil {
 		return stat.Size(), stat.ModTime(), nil
@@ -50,5 +84,7 @@ func (df *DiskFile) Name() string {
 }
 
 func (df *DiskFile) Sync() error {
+	df.fileSize = 0
+	df.bufWriterAt.Flush()
 	return df.File.Sync()
 }
diff --git a/weed/util/buffered_writer/max_latency_writer.go b/weed/util/buffered_writer/max_latency_writer.go
new file mode 100644
index 000000000..d95d26ffd
--- /dev/null
+++ b/weed/util/buffered_writer/max_latency_writer.go
@@ -0,0 +1,167 @@
+package buffered_writer
+
+import (
+	"io"
+	"sync"
+	"time"
+)
+
+type TimedWriteBuffer struct {
+	maxLatencyWriterAt *maxLatencyWriterAt
+	bufWriterAt        *bufferedWriterAt
+}
+
+func (t *TimedWriteBuffer) ReadAt(p []byte, off int64) (n int, err error) {
+	bufStart := t.bufWriterAt.nextOffset - int64(t.bufWriterAt.dataSize)
+	start := max(bufStart, off)
+	stop := min(t.bufWriterAt.nextOffset, off+int64(len(p)))
+	if start <= stop {
+		n = copy(p, t.bufWriterAt.data[start-bufStart:stop-bufStart])
+	}
+	return
+}
+func (t *TimedWriteBuffer) WriteAt(p []byte, offset int64) (n int, err error) {
+	return t.maxLatencyWriterAt.WriteAt(p, offset)
+}
+func (t *TimedWriteBuffer) Flush() {
+	t.maxLatencyWriterAt.Flush()
+}
+func (t *TimedWriteBuffer) Close() {
+	t.maxLatencyWriterAt.Close()
+}
+
+func NewTimedWriteBuffer(writerAt io.WriterAt, size int, latency time.Duration, currentOffset int64) *TimedWriteBuffer {
+	bufWriterAt := newBufferedWriterAt(writerAt, size, currentOffset)
+	maxLatencyWriterAt := newMaxLatencyWriterAt(bufWriterAt, latency)
+	return &TimedWriteBuffer{
+		bufWriterAt:        bufWriterAt,
+		maxLatencyWriterAt: maxLatencyWriterAt,
+	}
+}
+
+type bufferedWriterAt struct {
+	data       []byte
+	dataSize   int
+	nextOffset int64
+	writerAt   io.WriterAt
+	counter    int
+}
+
+func newBufferedWriterAt(writerAt io.WriterAt, bufferSize int, currentOffset int64) *bufferedWriterAt {
+	return &bufferedWriterAt{
+		data:       make([]byte, bufferSize),
+		nextOffset: currentOffset,
+		dataSize:   0,
+		writerAt:   writerAt,
+	}
+}
+
+func (b *bufferedWriterAt) WriteAt(p []byte, offset int64) (n int, err error) {
+	if b.nextOffset != offset {
+		println("nextOffset", b.nextOffset, "bufSize", b.dataSize, "offset", offset, "data", len(p))
+	}
+	if b.nextOffset != offset || len(p)+b.dataSize > len(b.data) {
+		if err = b.Flush(); err != nil {
+			return 0, err
+		}
+	}
+	if len(p)+b.dataSize > len(b.data) {
+		n, err = b.writerAt.WriteAt(p, offset)
+		if err == nil {
+			b.nextOffset = offset + int64(n)
+		}
+	} else {
+		n = copy(b.data[b.dataSize:len(p)+b.dataSize], p)
+		b.dataSize += n
+		b.nextOffset += int64(n)
+		b.counter++
+	}
+	return
+}
+
+func (b *bufferedWriterAt) Flush() (err error) {
+	if b.dataSize == 0 {
+		return nil
+	}
+	// println("flush", b.counter)
+	b.counter = 0
+	_, err = b.writerAt.WriteAt(b.data[0:b.dataSize], b.nextOffset-int64(b.dataSize))
+	if err == nil {
+		b.dataSize = 0
+	}
+	return
+}
+
+// adapted from https://golang.org/src/net/http/httputil/reverseproxy.go
+
+type writeFlusher interface {
+	io.WriterAt
+	Flush() error
+}
+
+type maxLatencyWriterAt struct {
+	dst          writeFlusher
+	latency      time.Duration // non-zero; negative means to flush immediately
+	mu           sync.Mutex    // protects t, flushPending, and dst.Flush
+	t            *time.Timer
+	flushPending bool
+}
+
+func newMaxLatencyWriterAt(dst writeFlusher, latency time.Duration) *maxLatencyWriterAt {
+	return &maxLatencyWriterAt{
+		dst:     dst,
+		latency: latency,
+	}
+}
+
+func (m *maxLatencyWriterAt) WriteAt(p []byte, offset int64) (n int, err error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	n, err = m.dst.WriteAt(p, offset)
+	if m.latency < 0 {
+		m.dst.Flush()
+		return
+	}
+	if m.flushPending {
+		return
+	}
+	if m.t == nil {
+		m.t = time.AfterFunc(m.latency, m.Flush)
+	} else {
+		m.t.Reset(m.latency)
+	}
+	m.flushPending = true
+	return
+}
+
+func (m *maxLatencyWriterAt) Flush() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if !m.flushPending { // if stop was called but AfterFunc already started this goroutine
+		return
+	}
+	m.dst.Flush()
+	m.flushPending = false
+}
+
+func (m *maxLatencyWriterAt) Close() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.flushPending = false
+	if m.t != nil {
+		m.t.Stop()
+	}
+}
+
+func min(x, y int64) int64 {
+	if x <= y {
+		return x
+	}
+	return y
+}
+func max(x, y int64) int64 {
+	if x <= y {
+		return y
+	}
+	return x
+}