diff --git a/weed/server/master_grpc_server_assign.go b/weed/server/master_grpc_server_assign.go
new file mode 100644
index 000000000..b55d6a80e
--- /dev/null
+++ b/weed/server/master_grpc_server_assign.go
@@ -0,0 +1,103 @@
+package weed_server
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/seaweedfs/raft"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
+	"github.com/seaweedfs/seaweedfs/weed/security"
+	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
+	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
+	"github.com/seaweedfs/seaweedfs/weed/topology"
+)
+
+func (ms *MasterServer) Assign(ctx context.Context, req *master_pb.AssignRequest) (*master_pb.AssignResponse, error) {
+
+	if !ms.Topo.IsLeader() {
+		return nil, raft.NotLeaderError
+	}
+
+	if req.Count == 0 {
+		req.Count = 1
+	}
+
+	if req.Replication == "" {
+		req.Replication = ms.option.DefaultReplicaPlacement
+	}
+	replicaPlacement, err := super_block.NewReplicaPlacementFromString(req.Replication)
+	if err != nil {
+		return nil, err
+	}
+	ttl, err := needle.ReadTTL(req.Ttl)
+	if err != nil {
+		return nil, err
+	}
+	diskType := types.ToDiskType(req.DiskType)
+
+	option := &topology.VolumeGrowOption{
+		Collection:         req.Collection,
+		ReplicaPlacement:   replicaPlacement,
+		Ttl:                ttl,
+		DiskType:           diskType,
+		Preallocate:        ms.preallocateSize,
+		DataCenter:         req.DataCenter,
+		Rack:               req.Rack,
+		DataNode:           req.DataNode,
+		MemoryMapMaxSizeMb: req.MemoryMapMaxSizeMb,
+	}
+
+	vl := ms.Topo.GetVolumeLayout(option.Collection, option.ReplicaPlacement, option.Ttl, option.DiskType)
+
+	if !vl.HasGrowRequest() && vl.ShouldGrowVolumes(option) {
+		if ms.Topo.AvailableSpaceFor(option) <= 0 {
+			return nil, fmt.Errorf("no free volumes left for " + option.String())
+		}
+		vl.AddGrowRequest()
+		ms.vgCh <- &topology.VolumeGrowRequest{
+			Option: option,
+			Count:  int(req.WritableVolumeCount),
+		}
+	}
+
+	var (
+		lastErr    error
+		maxTimeout = time.Second * 10
+		startTime  = time.Now()
+	)
+
+	for time.Now().Sub(startTime) < maxTimeout {
+		fid, count, dnList, err := ms.Topo.PickForWrite(req.Count, option)
+		if err == nil {
+			dn := dnList.Head()
+			var replicas []*master_pb.Location
+			for _, r := range dnList.Rest() {
+				replicas = append(replicas, &master_pb.Location{
+					Url:        r.Url(),
+					PublicUrl:  r.PublicUrl,
+					GrpcPort:   uint32(r.GrpcPort),
+					DataCenter: r.GetDataCenterId(),
+				})
+			}
+			return &master_pb.AssignResponse{
+				Fid: fid,
+				Location: &master_pb.Location{
+					Url:        dn.Url(),
+					PublicUrl:  dn.PublicUrl,
+					GrpcPort:   uint32(dn.GrpcPort),
+					DataCenter: dn.GetDataCenterId(),
+				},
+				Count:    count,
+				Auth:     string(security.GenJwtForVolumeServer(ms.guard.SigningKey, ms.guard.ExpiresAfterSec, fid)),
+				Replicas: replicas,
+			}, nil
+		}
+		//glog.V(4).Infoln("waiting for volume growing...")
+		lastErr = err
+		time.Sleep(200 * time.Millisecond)
+	}
+	return nil, lastErr
+}
diff --git a/weed/server/master_grpc_server_volume.go b/weed/server/master_grpc_server_volume.go
index 87c7b9990..4fa6406a7 100644
--- a/weed/server/master_grpc_server_volume.go
+++ b/weed/server/master_grpc_server_volume.go
@@ -16,7 +16,6 @@ import (
 	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
 	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
 	"github.com/seaweedfs/seaweedfs/weed/storage/types"
-	"github.com/seaweedfs/seaweedfs/weed/topology"
 )
 
 func (ms *MasterServer) ProcessGrowRequest() {
@@ -113,93 +112,6 @@ func (ms *MasterServer) LookupVolume(ctx context.Context, req *master_pb.LookupV
 	return resp, nil
 }
 
-func (ms *MasterServer) Assign(ctx context.Context, req *master_pb.AssignRequest) (*master_pb.AssignResponse, error) {
-
-	if !ms.Topo.IsLeader() {
-		return nil, raft.NotLeaderError
-	}
-
-	if req.Count == 0 {
-		req.Count = 1
-	}
-
-	if req.Replication == "" {
-		req.Replication = ms.option.DefaultReplicaPlacement
-	}
-	replicaPlacement, err := super_block.NewReplicaPlacementFromString(req.Replication)
-	if err != nil {
-		return nil, err
-	}
-	ttl, err := needle.ReadTTL(req.Ttl)
-	if err != nil {
-		return nil, err
-	}
-	diskType := types.ToDiskType(req.DiskType)
-
-	option := &topology.VolumeGrowOption{
-		Collection:         req.Collection,
-		ReplicaPlacement:   replicaPlacement,
-		Ttl:                ttl,
-		DiskType:           diskType,
-		Preallocate:        ms.preallocateSize,
-		DataCenter:         req.DataCenter,
-		Rack:               req.Rack,
-		DataNode:           req.DataNode,
-		MemoryMapMaxSizeMb: req.MemoryMapMaxSizeMb,
-	}
-
-	vl := ms.Topo.GetVolumeLayout(option.Collection, option.ReplicaPlacement, option.Ttl, option.DiskType)
-
-	if !vl.HasGrowRequest() && vl.ShouldGrowVolumes(option) {
-		if ms.Topo.AvailableSpaceFor(option) <= 0 {
-			return nil, fmt.Errorf("no free volumes left for " + option.String())
-		}
-		vl.AddGrowRequest()
-		ms.vgCh <- &topology.VolumeGrowRequest{
-			Option: option,
-			Count:  int(req.WritableVolumeCount),
-		}
-	}
-
-	var (
-		lastErr    error
-		maxTimeout = time.Second * 10
-		startTime  = time.Now()
-	)
-
-	for time.Now().Sub(startTime) < maxTimeout {
-		fid, count, dnList, err := ms.Topo.PickForWrite(req.Count, option)
-		if err == nil {
-			dn := dnList.Head()
-			var replicas []*master_pb.Location
-			for _, r := range dnList.Rest() {
-				replicas = append(replicas, &master_pb.Location{
-					Url:        r.Url(),
-					PublicUrl:  r.PublicUrl,
-					GrpcPort:   uint32(r.GrpcPort),
-					DataCenter: r.GetDataCenterId(),
-				})
-			}
-			return &master_pb.AssignResponse{
-				Fid: fid,
-				Location: &master_pb.Location{
-					Url:        dn.Url(),
-					PublicUrl:  dn.PublicUrl,
-					GrpcPort:   uint32(dn.GrpcPort),
-					DataCenter: dn.GetDataCenterId(),
-				},
-				Count:    count,
-				Auth:     string(security.GenJwtForVolumeServer(ms.guard.SigningKey, ms.guard.ExpiresAfterSec, fid)),
-				Replicas: replicas,
-			}, nil
-		}
-		//glog.V(4).Infoln("waiting for volume growing...")
-		lastErr = err
-		time.Sleep(200 * time.Millisecond)
-	}
-	return nil, lastErr
-}
-
 func (ms *MasterServer) Statistics(ctx context.Context, req *master_pb.StatisticsRequest) (*master_pb.StatisticsResponse, error) {
 
 	if !ms.Topo.IsLeader() {