diff --git a/weed/command/scaffold.go b/weed/command/scaffold.go
index 7a988cdcf..6fa72c730 100644
--- a/weed/command/scaffold.go
+++ b/weed/command/scaffold.go
@@ -346,5 +346,12 @@ scripts = """
 """
 sleep_minutes = 17          # sleep minutes between each script execution
 
+sequencer_type = memory     # Choose [memory|etcd] type for storing the file id sequence
+
+# when sequencer.type = etcd, set listen client urls of etcd cluster that store file id sequence
+# example : http://127.0.0.1:2379,http://127.0.0.1:2389
+sequencer_etcd_urls = http://127.0.0.1:2379
+
+
 `
 )
diff --git a/weed/operation/assign_file_id.go b/weed/operation/assign_file_id.go
index 4c50eaa26..2971cddbb 100644
--- a/weed/operation/assign_file_id.go
+++ b/weed/operation/assign_file_id.go
@@ -11,13 +11,14 @@ import (
 )
 
 type VolumeAssignRequest struct {
-	Count       uint64
-	Replication string
-	Collection  string
-	Ttl         string
-	DataCenter  string
-	Rack        string
-	DataNode    string
+	Count               uint64
+	Replication         string
+	Collection          string
+	Ttl                 string
+	DataCenter          string
+	Rack                string
+	DataNode            string
+	WritableVolumeCount uint32
 }
 
 type AssignResult struct {
@@ -53,6 +54,7 @@ func Assign(server string, grpcDialOption grpc.DialOption, primaryRequest *Volum
 				DataCenter:  primaryRequest.DataCenter,
 				Rack:        primaryRequest.Rack,
 				DataNode:    primaryRequest.DataNode,
+				WritableVolumeCount: primaryRequest.WritableVolumeCount,
 			}
 			resp, grpcErr := masterClient.Assign(context.Background(), req)
 			if grpcErr != nil {
diff --git a/weed/pb/master.proto b/weed/pb/master.proto
index 80231a2d8..f03b3a9ab 100644
--- a/weed/pb/master.proto
+++ b/weed/pb/master.proto
@@ -140,6 +140,7 @@ message AssignRequest {
     string rack = 6;
     string data_node = 7;
     uint32 memory_map_max_size_mb = 8;
+    uint32 Writable_volume_count = 9;
 }
 message AssignResponse {
     string fid = 1;
diff --git a/weed/pb/master_pb/master.pb.go b/weed/pb/master_pb/master.pb.go
index 880d39de5..e9fe8164c 100644
--- a/weed/pb/master_pb/master.pb.go
+++ b/weed/pb/master_pb/master.pb.go
@@ -648,14 +648,15 @@ func (m *Location) GetPublicUrl() string {
 }
 
 type AssignRequest struct {
-	Count              uint64 `protobuf:"varint,1,opt,name=count" json:"count,omitempty"`
-	Replication        string `protobuf:"bytes,2,opt,name=replication" json:"replication,omitempty"`
-	Collection         string `protobuf:"bytes,3,opt,name=collection" json:"collection,omitempty"`
-	Ttl                string `protobuf:"bytes,4,opt,name=ttl" json:"ttl,omitempty"`
-	DataCenter         string `protobuf:"bytes,5,opt,name=data_center,json=dataCenter" json:"data_center,omitempty"`
-	Rack               string `protobuf:"bytes,6,opt,name=rack" json:"rack,omitempty"`
-	DataNode           string `protobuf:"bytes,7,opt,name=data_node,json=dataNode" json:"data_node,omitempty"`
-	MemoryMapMaxSizeMb uint32 `protobuf:"varint,8,opt,name=memory_map_max_size_mb,json=MemoryMapMaxSizeMb" json:"memory_map_max_size_mb,omitempty"`
+	Count               uint64 `protobuf:"varint,1,opt,name=count" json:"count,omitempty"`
+	Replication         string `protobuf:"bytes,2,opt,name=replication" json:"replication,omitempty"`
+	Collection          string `protobuf:"bytes,3,opt,name=collection" json:"collection,omitempty"`
+	Ttl                 string `protobuf:"bytes,4,opt,name=ttl" json:"ttl,omitempty"`
+	DataCenter          string `protobuf:"bytes,5,opt,name=data_center,json=dataCenter" json:"data_center,omitempty"`
+	Rack                string `protobuf:"bytes,6,opt,name=rack" json:"rack,omitempty"`
+	DataNode            string `protobuf:"bytes,7,opt,name=data_node,json=dataNode" json:"data_node,omitempty"`
+	MemoryMapMaxSizeMb  uint32 `protobuf:"varint,8,opt,name=memory_map_max_size_mb,json=memoryMapMaxSizeMb" json:"memory_map_max_size_mb,omitempty"`
+	WritableVolumeCount uint32 `protobuf:"varint,9,opt,name=Writable_volume_count,json=WritableVolumeCount" json:"Writable_volume_count,omitempty"`
 }
 
 func (m *AssignRequest) Reset()                    { *m = AssignRequest{} }
@@ -719,6 +720,13 @@ func (m *AssignRequest) GetMemoryMapMaxSizeMb() uint32 {
 	return 0
 }
 
+func (m *AssignRequest) GetWritableVolumeCount() uint32 {
+	if m != nil {
+		return m.WritableVolumeCount
+	}
+	return 0
+}
+
 type AssignResponse struct {
 	Fid       string `protobuf:"bytes,1,opt,name=fid" json:"fid,omitempty"`
 	Url       string `protobuf:"bytes,2,opt,name=url" json:"url,omitempty"`
@@ -1809,125 +1817,127 @@ var _Seaweed_serviceDesc = grpc.ServiceDesc{
 func init() { proto.RegisterFile("master.proto", fileDescriptor0) }
 
 var fileDescriptor0 = []byte{
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+	0x50, 0xa6, 0xf3, 0xf2, 0x19, 0x6c, 0x07, 0xb1, 0x17, 0x4e, 0x7d, 0xe2, 0xc6, 0x7c, 0x00, 0x86,
+	0x39, 0xaf, 0xb6, 0x04, 0x1d, 0xd9, 0x52, 0xda, 0x67, 0x42, 0xa9, 0xf9, 0xf5, 0xc7, 0x80, 0xf4,
+	0x2a, 0xe2, 0xe5, 0x2b, 0x2a, 0x62, 0x45, 0x4f, 0x69, 0x0e, 0x3d, 0x65, 0x6d, 0xbf, 0x80, 0xed,
+	0xc5, 0xcd, 0x55, 0xaa, 0x7e, 0x04, 0xad, 0x02, 0x76, 0xdd, 0x07, 0x6f, 0x1b, 0xed, 0xa7, 0x58,
+	0xe7, 0x98, 0x96, 0xf6, 0xf7, 0xe1, 0xbd, 0x42, 0xf5, 0x58, 0x34, 0xfa, 0xab, 0x06, 0xd0, 0x10,
+	0x06, 0xcb, 0xe6, 0x32, 0x06, 0xfb, 0xdf, 0x15, 0x68, 0x3f, 0x56, 0x95, 0xcb, 0x59, 0x80, 0x31,
+	0xf7, 0x9b, 0x62, 0xee, 0xdf, 0x87, 0x76, 0xa9, 0x20, 0x25, 0xa1, 0x6c, 0x5d, 0x18, 0x17, 0xbd,
+	0x55, 0x57, 0xc2, 0xaa, 0x30, 0x5b, 0xbc, 0x12, 0x3e, 0x80, 0xfe, 0x49, 0x46, 0xc8, 0xf2, 0xed,
+	0xb1, 0xe6, 0x6c, 0x70, 0x85, 0x69, 0xbb, 0x07, 0x9b, 0xd8, 0x63, 0xc1, 0xc5, 0x82, 0xb5, 0x3c,
+	0x5f, 0x7d, 0xa9, 0x32, 0xed, 0xbf, 0xc8, 0x03, 0x0d, 0xe2, 0x93, 0x84, 0x0e, 0xea, 0x6f, 0x7e,
+	0xfb, 0x53, 0x5f, 0xc3, 0x35, 0x14, 0x3d, 0x87, 0xae, 0xbe, 0x45, 0x28, 0x4f, 0xeb, 0x37, 0xbe,
+	0xa1, 0xb4, 0x49, 0xa1, 0xa2, 0xf6, 0xef, 0x2b, 0xd0, 0x70, 0xb0, 0x77, 0xfe, 0x6e, 0xe3, 0xfb,
+	0x39, 0x6c, 0xe4, 0x3d, 0xbf, 0x04, 0xf1, 0x7b, 0x06, 0x30, 0xe6, 0x51, 0x72, 0x3a, 0xbe, 0xf1,
+	0x46, 0xed, 0xff, 0x59, 0xd0, 0x7d, 0x9c, 0xcf, 0x95, 0x77, 0x1b, 0x8c, 0x7d, 0x00, 0x3e, 0x08,
+	0x4b, 0x38, 0x98, 0xc4, 0x41, 0xa7, 0xdb, 0x69, 0x66, 0xea, 0x89, 0xda, 0x7f, 0xac, 0x40, 0xfb,
+	0x65, 0x92, 0x26, 0x61, 0x72, 0x3a, 0x7f, 0xb7, 0xbf, 0xfe, 0x10, 0xfa, 0x06, 0x67, 0x28, 0x81,
+	0x70, 0x67, 0xe1, 0x30, 0x14, 0xc9, 0x76, 0x36, 0xfc, 0xd2, 0x3b, 0xb5, 0x37, 0xa1, 0xaf, 0x78,
+	0x71, 0xd1, 0x92, 0xed, 0xdf, 0x59, 0x80, 0x4c, 0xa9, 0xea, 0x95, 0x3f, 0x85, 0x0e, 0x53, 0xd8,
+	0x89, 0xfd, 0xd4, 0xe5, 0xc0, 0x3c, 0x7b, 0x26, 0xb6, 0x4e, 0x9b, 0x99, 0x48, 0xff, 0x00, 0xb6,
+	0x96, 0x6e, 0xf8, 0x9c, 0x90, 0x48, 0x84, 0xfb, 0x0b, 0x97, 0xfc, 0xe3, 0x89, 0xfd, 0x19, 0xdc,
+	0x96, 0x24, 0x54, 0xf7, 0x71, 0xdd, 0x5f, 0x97, 0xd8, 0x64, 0xa7, 0x60, 0x93, 0xf6, 0x7f, 0x2d,
+	0xd8, 0x5e, 0x5c, 0xa6, 0xe2, 0xbf, 0x6a, 0x1d, 0xc2, 0x80, 0x54, 0xbf, 0x31, 0x79, 0xb1, 0xa4,
+	0xa3, 0x9f, 0x2e, 0xf1, 0xe2, 0x45, 0xdf, 0x7b, 0xba, 0x0f, 0x15, 0xd4, 0xb8, 0x47, 0xcb, 0x02,
+	0x3a, 0xc4, 0xd0, 0x5f, 0x32, 0xe3, 0xb7, 0x0a, 0xbd, 0xaf, 0x8a, 0x69, 0x5d, 0x2d, 0xfc, 0x16,
+	0xc4, 0xd8, 0xde, 0x81, 0xbb, 0x5f, 0x12, 0x76, 0x2c, 0x6c, 0x0e, 0x92, 0xf8, 0x24, 0x38, 0x9d,
+	0x66, 0xd2, 0xa8, 0x48, 0xed, 0xbd, 0xcb, 0x2c, 0x14, 0x4c, 0x2b, 0x7e, 0x46, 0xb1, 0x6e, 0xfc,
+	0x33, 0x4a, 0xe5, 0xaa, 0x9f, 0x51, 0xf6, 0xff, 0x55, 0x87, 0xf5, 0x31, 0xc1, 0xaf, 0x09, 0xf1,
+	0xd1, 0x11, 0x74, 0xc6, 0x24, 0xf6, 0x8b, 0x1f, 0x48, 0xb7, 0x8c, 0x6f, 0xcc, 0xa5, 0xc3, 0xef,
+	0xac, 0x92, 0xe6, 0x23, 0xf4, 0xd6, 0xae, 0xf5, 0x89, 0x85, 0x5e, 0x40, 0xa7, 0x74, 0x23, 0x44,
+	0x3b, 0xc6, 0xa2, 0x55, 0x77, 0xc5, 0xe1, 0x9d, 0xa5, 0x81, 0xa2, 0x51, 0xcd, 0x5d, 0xb6, 0xcd,
+	0x9b, 0x10, 0xba, 0x77, 0xe9, 0x15, 0x49, 0x3a, 0xdc, 0xb9, 0xe6, 0x0a, 0x65, 0xdf, 0x42, 0x9f,
+	0x43, 0x5d, 0x52, 0x66, 0x34, 0x30, 0x8c, 0x4b, 0x77, 0x8f, 0x52, 0x5c, 0x65, 0x7e, 0x6d, 0xdf,
+	0x42, 0x4f, 0x00, 0x0a, 0xd2, 0x89, 0x4c, 0x60, 0x96, 0x58, 0xef, 0xf0, 0xee, 0x25, 0xda, 0xdc,
+	0xd9, 0xd7, 0xd0, 0x2d, 0x53, 0x23, 0x34, 0x5a, 0xc9, 0x7e, 0x8c, 0xfe, 0x30, 0xbc, 0x7f, 0x85,
+	0x45, 0xee, 0xf8, 0x57, 0xd0, 0x5b, 0x64, 0x3c, 0xc8, 0x5e, 0xb9, 0xb0, 0xc4, 0x9e, 0x86, 0x1f,
+	0x5c, 0x69, 0x63, 0x82, 0x50, 0xb4, 0xa8, 0x12, 0x08, 0x4b, 0xfd, 0xac, 0x04, 0xc2, 0x72, 0x5f,
+	0x93, 0x20, 0x94, 0xeb, 0xba, 0x04, 0xc2, 0xca, 0x2e, 0x54, 0x02, 0x61, 0x75, 0x53, 0xb0, 0x6f,
+	0xa1, 0x04, 0xb6, 0x57, 0x57, 0x1b, 0x32, 0x7f, 0x52, 0xb9, 0xb2, 0x64, 0x87, 0x1f, 0xbd, 0x81,
+	0xa5, 0xde, 0x70, 0x52, 0x17, 0xff, 0x3e, 0x7c, 0xfa, 0xff, 0x00, 0x00, 0x00, 0xff, 0xff, 0x44,
+	0x05, 0x7a, 0xc2, 0x8d, 0x18, 0x00, 0x00,
 }
diff --git a/weed/pb/volume_server_pb/volume_server.pb.go b/weed/pb/volume_server_pb/volume_server.pb.go
index f8af827a6..24907cdba 100644
--- a/weed/pb/volume_server_pb/volume_server.pb.go
+++ b/weed/pb/volume_server_pb/volume_server.pb.go
@@ -320,7 +320,7 @@ type AllocateVolumeRequest struct {
 	Preallocate        int64  `protobuf:"varint,3,opt,name=preallocate" json:"preallocate,omitempty"`
 	Replication        string `protobuf:"bytes,4,opt,name=replication" json:"replication,omitempty"`
 	Ttl                string `protobuf:"bytes,5,opt,name=ttl" json:"ttl,omitempty"`
-	MemoryMapMaxSizeMb uint32 `protobuf:"varint,6,opt,name=memory_map_max_size_mb,json=MemoryMapMaxSizeMb" json:"memory_map_max_size_mb,omitempty"`
+	MemoryMapMaxSizeMb uint32 `protobuf:"varint,6,opt,name=memory_map_max_size_mb,json=memoryMapMaxSizeMb" json:"memory_map_max_size_mb,omitempty"`
 }
 
 func (m *AllocateVolumeRequest) Reset()                    { *m = AllocateVolumeRequest{} }
diff --git a/weed/sequence/etcd_sequencer.go b/weed/sequence/etcd_sequencer.go
new file mode 100644
index 000000000..1fc378640
--- /dev/null
+++ b/weed/sequence/etcd_sequencer.go
@@ -0,0 +1,296 @@
+package sequence
+
+/*
+Note :
+(1) store the sequence in the ETCD cluster, and local file(sequence.dat)
+(2) batch get the sequences from ETCD cluster, and store the max sequence id in the local file
+(3) the sequence range is : [currentSeqId, maxSeqId), when the currentSeqId >= maxSeqId, fetch the new maxSeqId.
+*/
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+
+	"io"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"go.etcd.io/etcd/client"
+)
+
+const (
+	// EtcdKeyPrefix                   = "/seaweedfs"
+	EtcdKeySequence                 = "/master/sequence"
+	EtcdContextTimeoutSecond        = 100 * time.Second
+	DefaultEtcdSteps         uint64 = 500 // internal counter
+	SequencerFileName               = "sequencer.dat"
+	FileMaxSequenceLength           = 128
+)
+
+type EtcdSequencer struct {
+	sequenceLock sync.Mutex
+
+	// available sequence range : [currentSeqId, maxSeqId)
+	currentSeqId uint64
+	maxSeqId     uint64
+
+	keysAPI client.KeysAPI
+	seqFile *os.File
+}
+
+func NewEtcdSequencer(etcdUrls string, metaFolder string) (*EtcdSequencer, error) {
+	file, err := openSequenceFile(metaFolder + "/" + SequencerFileName)
+	if nil != err {
+		return nil, fmt.Errorf("open sequence file fialed, %v", err)
+	}
+
+	cli, err := client.New(client.Config{
+		Endpoints: strings.Split(etcdUrls, ","),
+		Username:  "",
+		Password:  "",
+	})
+	if err != nil {
+		return nil, err
+	}
+	keysApi := client.NewKeysAPI(cli)
+
+	// TODO: the current sequence id in local file is not used
+	maxValue, _, err := readSequenceFile(file)
+	if err != nil {
+		return nil, fmt.Errorf("read sequence from file failed, %v", err)
+	}
+	glog.V(4).Infof("read sequence from file : %d", maxValue)
+
+	newSeq, err := setMaxSequenceToEtcd(keysApi, maxValue)
+	if err != nil {
+		return nil, err
+	}
+
+	sequencer := &EtcdSequencer{maxSeqId: newSeq,
+		currentSeqId: newSeq,
+		keysAPI:      keysApi,
+		seqFile:      file,
+	}
+	return sequencer, nil
+}
+
+func (es *EtcdSequencer) NextFileId(count uint64) uint64 {
+	es.sequenceLock.Lock()
+	defer es.sequenceLock.Unlock()
+
+	if (es.currentSeqId + count) >= es.maxSeqId {
+		reqSteps := DefaultEtcdSteps
+		if count > DefaultEtcdSteps {
+			reqSteps += count
+		}
+		maxId, err := batchGetSequenceFromEtcd(es.keysAPI, reqSteps)
+		glog.V(4).Infof("get max sequence id from etcd, %d", maxId)
+		if err != nil {
+			glog.Error(err)
+			return 0
+		}
+		es.currentSeqId, es.maxSeqId = maxId-reqSteps, maxId
+		glog.V(4).Infof("current id : %d, max id : %d", es.currentSeqId, es.maxSeqId)
+
+		if err := writeSequenceFile(es.seqFile, es.maxSeqId, es.currentSeqId); err != nil {
+			glog.Errorf("flush sequence to file failed, %v", err)
+		}
+	}
+
+	ret := es.currentSeqId
+	es.currentSeqId += count
+	return ret
+}
+
+/**
+instead of collecting the max value from volume server,
+the max value should be saved in local config file and ETCD cluster
+*/
+func (es *EtcdSequencer) SetMax(seenValue uint64) {
+	es.sequenceLock.Lock()
+	defer es.sequenceLock.Unlock()
+	if seenValue > es.maxSeqId {
+		maxId, err := setMaxSequenceToEtcd(es.keysAPI, seenValue)
+		if err != nil {
+			glog.Errorf("set Etcd Max sequence failed : %v", err)
+			return
+		}
+		es.currentSeqId, es.maxSeqId = maxId, maxId
+
+		if err := writeSequenceFile(es.seqFile, maxId, maxId); err != nil {
+			glog.Errorf("flush sequence to file failed, %v", err)
+		}
+	}
+}
+
+func (es *EtcdSequencer) GetMax() uint64 {
+	return es.maxSeqId
+}
+
+func (es *EtcdSequencer) Peek() uint64 {
+	return es.currentSeqId
+}
+
+func batchGetSequenceFromEtcd(kvApi client.KeysAPI, step uint64) (uint64, error) {
+	if step <= 0 {
+		return 0, fmt.Errorf("the step must be large than 1")
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), EtcdContextTimeoutSecond)
+	var endSeqValue uint64 = 0
+	defer cancel()
+	for {
+		getResp, err := kvApi.Get(ctx, EtcdKeySequence, &client.GetOptions{Recursive: false, Quorum: true})
+		if err != nil {
+			return 0, err
+		}
+		if getResp.Node == nil {
+			continue
+		}
+
+		prevValue := getResp.Node.Value
+		prevSeqValue, err := strconv.ParseUint(prevValue, 10, 64)
+		if err != nil {
+			return 0, fmt.Errorf("get sequence from etcd failed, %v", err)
+		}
+		endSeqValue = prevSeqValue + step
+		endSeqStr := strconv.FormatUint(endSeqValue, 10)
+
+		_, err = kvApi.Set(ctx, EtcdKeySequence, endSeqStr, &client.SetOptions{PrevValue: prevValue})
+		if err == nil {
+			break
+		}
+		glog.Error(err)
+	}
+
+	return endSeqValue, nil
+}
+
+/**
+update the value of the key EtcdKeySequence in ETCD cluster with the parameter of maxSeq,
+when the value of the key EtcdKeySequence is equal to or large than the parameter maxSeq,
+return the value of EtcdKeySequence in the ETCD cluster;
+when the value of the EtcdKeySequence is less than the parameter maxSeq,
+return the value of the parameter maxSeq
+*/
+func setMaxSequenceToEtcd(kvApi client.KeysAPI, maxSeq uint64) (uint64, error) {
+	maxSeqStr := strconv.FormatUint(maxSeq, 10)
+	ctx, cancel := context.WithTimeout(context.Background(), EtcdContextTimeoutSecond)
+	defer cancel()
+
+	for {
+		getResp, err := kvApi.Get(ctx, EtcdKeySequence, &client.GetOptions{Recursive: false, Quorum: true})
+		if err != nil {
+			if ce, ok := err.(client.Error); ok && (ce.Code == client.ErrorCodeKeyNotFound) {
+				_, err := kvApi.Create(ctx, EtcdKeySequence, maxSeqStr)
+				if err == nil {
+					continue
+				}
+				if ce, ok = err.(client.Error); ok && (ce.Code == client.ErrorCodeNodeExist) {
+					continue
+				}
+				return 0, err
+			} else {
+				return 0, err
+			}
+		}
+
+		if getResp.Node == nil {
+			continue
+		}
+		prevSeqStr := getResp.Node.Value
+		prevSeq, err := strconv.ParseUint(prevSeqStr, 10, 64)
+		if err != nil {
+			return 0, err
+		}
+		if prevSeq >= maxSeq {
+			return prevSeq, nil
+		}
+
+		_, err = kvApi.Set(ctx, EtcdKeySequence, maxSeqStr, &client.SetOptions{PrevValue: prevSeqStr})
+		if err != nil {
+			return 0, err
+		}
+	}
+}
+
+func openSequenceFile(file string) (*os.File, error) {
+	_, err := os.Stat(file)
+	if os.IsNotExist(err) {
+		fid, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE, 0644)
+		if err != nil {
+			return nil, err
+		}
+		if err := writeSequenceFile(fid, 1, 0); err != nil {
+			return nil, err
+		}
+		return fid, nil
+	} else {
+		return os.OpenFile(file, os.O_RDWR|os.O_CREATE, 0644)
+	}
+}
+
+/*
+read sequence and step from sequence file
+*/
+func readSequenceFile(file *os.File) (uint64, uint64, error) {
+	sequence := make([]byte, FileMaxSequenceLength)
+	size, err := file.ReadAt(sequence, 0)
+	if (err != nil) && (err != io.EOF) {
+		err := fmt.Errorf("cannot read file %s, %v", file.Name(), err)
+		return 0, 0, err
+	}
+	sequence = sequence[0:size]
+	seqs := strings.Split(string(sequence), ":")
+	maxId, err := strconv.ParseUint(seqs[0], 10, 64)
+	if err != nil {
+		return 0, 0, fmt.Errorf("parse sequence from file failed, %v", err)
+	}
+
+	if len(seqs) > 1 {
+		step, err := strconv.ParseUint(seqs[1], 10, 64)
+		if err != nil {
+			return 0, 0, fmt.Errorf("parse sequence from file failed, %v", err)
+		}
+		return maxId, step, nil
+	}
+
+	return maxId, 0, nil
+}
+
+/**
+write the sequence and step to sequence file
+*/
+func writeSequenceFile(file *os.File, sequence, step uint64) error {
+	_ = step
+	seqStr := fmt.Sprintf("%d:%d", sequence, sequence)
+	if _, err := file.Seek(0, 0); err != nil {
+		err = fmt.Errorf("cannot seek to the beginning of %s: %v", file.Name(), err)
+		return err
+	}
+	if err := file.Truncate(0); err != nil {
+		return fmt.Errorf("truncate sequence file faield : %v", err)
+	}
+	if _, err := file.WriteString(seqStr); err != nil {
+		return fmt.Errorf("write file %s failed, %v", file.Name(), err)
+	}
+	if err := file.Sync(); err != nil {
+		return fmt.Errorf("flush file %s failed, %v", file.Name(), err)
+	}
+	return nil
+}
+
+// the UT helper method
+// func deleteEtcdKey(kvApi client.KeysAPI, key string) error {
+// 	ctx, cancel := context.WithTimeout(context.Background(), EtcdContextTimeoutSecond)
+// 	defer cancel()
+// 	_, err := kvApi.Delete(ctx, key, &client.DeleteOptions{Dir: false})
+// 	if err != nil {
+// 		return err
+// 	}
+// 	return nil
+// }
diff --git a/weed/server/master_grpc_server_volume.go b/weed/server/master_grpc_server_volume.go
index 0580acf76..8fc56e9b8 100644
--- a/weed/server/master_grpc_server_volume.go
+++ b/weed/server/master_grpc_server_volume.go
@@ -78,7 +78,7 @@ func (ms *MasterServer) Assign(ctx context.Context, req *master_pb.AssignRequest
 		}
 		ms.vgLock.Lock()
 		if !ms.Topo.HasWritableVolume(option) {
-			if _, err = ms.vg.AutomaticGrowByType(option, ms.grpcDialOption, ms.Topo); err != nil {
+			if _, err = ms.vg.AutomaticGrowByType(option, ms.grpcDialOption, ms.Topo, int(req.WritableVolumeCount)); err != nil {
 				ms.vgLock.Unlock()
 				return nil, fmt.Errorf("Cannot grow volume group! %v", err)
 			}
diff --git a/weed/server/master_server.go b/weed/server/master_server.go
index cde583560..15e6ee51c 100644
--- a/weed/server/master_server.go
+++ b/weed/server/master_server.go
@@ -27,6 +27,12 @@ import (
 	"google.golang.org/grpc"
 )
 
+const (
+	MasterPrefix      = "master.maintenance"
+	SequencerType     = MasterPrefix + ".sequencer_type"
+	SequencerEtcdUrls = MasterPrefix + ".sequencer_etcd_urls"
+)
+
 type MasterOption struct {
 	Port                    int
 	MetaFolder              string
@@ -87,7 +93,11 @@ func NewMasterServer(r *mux.Router, option *MasterOption, peers []string) *Maste
 		MasterClient:    wdclient.NewMasterClient(context.Background(), grpcDialOption, "master", peers),
 	}
 	ms.bounedLeaderChan = make(chan int, 16)
-	seq := sequence.NewMemorySequencer()
+
+	seq := ms.createSequencer(option)
+	if nil == seq {
+		glog.Fatalf("create sequencer failed.")
+	}
 	ms.Topo = topology.NewTopology("topo", seq, uint64(ms.option.VolumeSizeLimitMB)*1024*1024, ms.option.PulseSeconds)
 	ms.vg = topology.NewDefaultVolumeGrowth()
 	glog.V(0).Infoln("Volume Size Limit is", ms.option.VolumeSizeLimitMB, "MB")
@@ -165,8 +175,8 @@ func (ms *MasterServer) proxyToLeader(f func(w http.ResponseWriter, r *http.Requ
 			proxy.Transport = util.Transport
 			proxy.ServeHTTP(w, r)
 		} else {
-			//drop it to the floor
-			//writeJsonError(w, r, errors.New(ms.Topo.RaftServer.Name()+" does not know Leader yet:"+ms.Topo.RaftServer.Leader()))
+			// drop it to the floor
+			// writeJsonError(w, r, errors.New(ms.Topo.RaftServer.Name()+" does not know Leader yet:"+ms.Topo.RaftServer.Leader()))
 		}
 	}
 }
@@ -230,3 +240,25 @@ func (ms *MasterServer) startAdminScripts() {
 		}
 	}()
 }
+
+func (ms *MasterServer) createSequencer(option *MasterOption) sequence.Sequencer {
+	var seq sequence.Sequencer
+	seqType := strings.ToLower(util.Config().GetString(SequencerType))
+	glog.V(0).Infof("[%s] : [%s]", SequencerType, seqType)
+	switch strings.ToLower(seqType) {
+	case "memory":
+		seq = sequence.NewMemorySequencer()
+	case "etcd":
+		var err error
+		urls := util.Config().GetString(SequencerEtcdUrls)
+		glog.V(0).Infof("[%s] : [%s]", SequencerEtcdUrls, urls)
+		seq, err = sequence.NewEtcdSequencer(urls, option.MetaFolder)
+		if err != nil {
+			glog.Error(err)
+			seq = nil
+		}
+	default:
+		seq = sequence.NewMemorySequencer()
+	}
+	return seq
+}
diff --git a/weed/server/master_server_handlers.go b/weed/server/master_server_handlers.go
index 9bcd35ced..514d86800 100644
--- a/weed/server/master_server_handlers.go
+++ b/weed/server/master_server_handlers.go
@@ -100,6 +100,11 @@ func (ms *MasterServer) dirAssignHandler(w http.ResponseWriter, r *http.Request)
 		requestedCount = 1
 	}
 
+	writableVolumeCount, e := strconv.Atoi(r.FormValue("writableVolumeCount"))
+	if e != nil {
+		writableVolumeCount = 0
+	}
+
 	option, err := ms.getVolumeGrowOption(r)
 	if err != nil {
 		writeJsonQuiet(w, r, http.StatusNotAcceptable, operation.AssignResult{Error: err.Error()})
@@ -114,7 +119,7 @@ func (ms *MasterServer) dirAssignHandler(w http.ResponseWriter, r *http.Request)
 		ms.vgLock.Lock()
 		defer ms.vgLock.Unlock()
 		if !ms.Topo.HasWritableVolume(option) {
-			if _, err = ms.vg.AutomaticGrowByType(option, ms.grpcDialOption, ms.Topo); err != nil {
+			if _, err = ms.vg.AutomaticGrowByType(option, ms.grpcDialOption, ms.Topo, writableVolumeCount); err != nil {
 				writeJsonError(w, r, http.StatusInternalServerError,
 					fmt.Errorf("Cannot grow volume group! %v", err))
 				return
diff --git a/weed/shell/command_ec_balance.go b/weed/shell/command_ec_balance.go
index 47ae7bad3..8bf993f4a 100644
--- a/weed/shell/command_ec_balance.go
+++ b/weed/shell/command_ec_balance.go
@@ -266,6 +266,10 @@ func doBalanceEcShardsAcrossRacks(ctx context.Context, commandEnv *CommandEnv, c
 
 	for shardId, ecNode := range ecShardsToMove {
 		rackId := pickOneRack(racks, rackToShardCount, averageShardsPerEcRack)
+		if rackId == "" {
+			fmt.Printf("ec shard %d.%d at %s can not find a destination rack\n", vid, shardId, ecNode.info.Id)
+			continue
+		}
 		var possibleDestinationEcNodes []*EcNode
 		for _, n := range racks[rackId].ecNodes {
 			possibleDestinationEcNodes = append(possibleDestinationEcNodes, n)
diff --git a/weed/shell/command_ec_common.go b/weed/shell/command_ec_common.go
index d0fe16a68..1e9d96212 100644
--- a/weed/shell/command_ec_common.go
+++ b/weed/shell/command_ec_common.go
@@ -156,7 +156,7 @@ func countShards(ecShardInfos []*master_pb.VolumeEcShardInformationMessage) (cou
 }
 
 func countFreeShardSlots(dn *master_pb.DataNodeInfo) (count int) {
-	return int(dn.FreeVolumeCount)*10 - countShards(dn.EcShardInfos)
+	return int(dn.FreeVolumeCount)*erasure_coding.DataShardsCount - countShards(dn.EcShardInfos)
 }
 
 type RackId string
diff --git a/weed/topology/volume_growth.go b/weed/topology/volume_growth.go
index f21ab45ef..636eb2260 100644
--- a/weed/topology/volume_growth.go
+++ b/weed/topology/volume_growth.go
@@ -59,8 +59,11 @@ func (vg *VolumeGrowth) findVolumeCount(copyCount int) (count int) {
 	return
 }
 
-func (vg *VolumeGrowth) AutomaticGrowByType(option *VolumeGrowOption, grpcDialOption grpc.DialOption, topo *Topology) (count int, err error) {
-	count, err = vg.GrowByCountAndType(grpcDialOption, vg.findVolumeCount(option.ReplicaPlacement.GetCopyCount()), option, topo)
+func (vg *VolumeGrowth) AutomaticGrowByType(option *VolumeGrowOption, grpcDialOption grpc.DialOption, topo *Topology, targetCount int) (count int, err error) {
+	if targetCount == 0 {
+		targetCount = vg.findVolumeCount(option.ReplicaPlacement.GetCopyCount())
+	}
+	count, err = vg.GrowByCountAndType(grpcDialOption, targetCount, option, topo)
 	if count > 0 && count%option.ReplicaPlacement.GetCopyCount() == 0 {
 		return count, nil
 	}
diff --git a/weed/util/config.go b/weed/util/config.go
index 1ea833d1f..7e2f9b373 100644
--- a/weed/util/config.go
+++ b/weed/util/config.go
@@ -40,5 +40,9 @@ func LoadConfiguration(configFileName string, required bool) (loaded bool) {
 	}
 
 	return true
-
 }
+
+func Config() Configuration {
+	return viper.GetViper()
+}
+