diff --git a/weed/command/benchmark.go b/weed/command/benchmark.go
index 7e0802e30..7bbb82319 100644
--- a/weed/command/benchmark.go
+++ b/weed/command/benchmark.go
@@ -205,7 +205,11 @@ func writeFiles(idChan chan int, fileIdLineChan chan string, s *stat) {
 		start := time.Now()
 		fileSize := int64(*b.fileSize + rand.Intn(64))
 		fp := &operation.FilePart{Reader: &FakeReader{id: uint64(id), size: fileSize}, FileSize: fileSize}
-		if assignResult, err := operation.Assign(*b.server, 1, "", *b.collection, ""); err == nil {
+		ar := &operation.VolumeAssignRequest{
+			Count:      1,
+			Collection: *b.collection,
+		}
+		if assignResult, err := operation.Assign(*b.server, ar); err == nil {
 			fp.Server, fp.Fid, fp.Collection = assignResult.Url, assignResult.Fid, *b.collection
 			if _, err := fp.Upload(0, *b.server, secret); err == nil {
 				if rand.Intn(100) < *b.deletePercentage {
diff --git a/weed/operation/assign_file_id.go b/weed/operation/assign_file_id.go
index a893e836b..f2365890c 100644
--- a/weed/operation/assign_file_id.go
+++ b/weed/operation/assign_file_id.go
@@ -11,6 +11,16 @@ import (
 	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
+type VolumeAssignRequest struct {
+	Count       uint64
+	Replication string
+	Collection  string
+	Ttl         string
+	DataCenter  string
+	Rack        string
+	DataNode    string
+}
+
 type AssignResult struct {
 	Fid       string `json:"fid,omitempty"`
 	Url       string `json:"url,omitempty"`
@@ -19,47 +29,26 @@ type AssignResult struct {
 	Error     string `json:"error,omitempty"`
 }
 
-/*
-options params meaning:
-options[0] main data Center
-options[1] main rack
-options[2] main data node
-*/
-func Assign(server string, count uint64, replication string, collection string, ttl string, options ...string) (*AssignResult, error) {
+func Assign(server string, r *VolumeAssignRequest) (*AssignResult, error) {
 	values := make(url.Values)
-	values.Add("count", strconv.FormatUint(count, 10))
-	if replication != "" {
-		values.Add("replication", replication)
+	values.Add("count", strconv.FormatUint(r.Count, 10))
+	if r.Replication != "" {
+		values.Add("replication", r.Replication)
 	}
-	if collection != "" {
-		values.Add("collection", collection)
+	if r.Collection != "" {
+		values.Add("collection", r.Collection)
 	}
-	if ttl != "" {
-		values.Add("ttl", ttl)
+	if r.Ttl != "" {
+		values.Add("ttl", r.Ttl)
 	}
-
-	var dataCenter, rack, dataNode string
-	switch len(options) {
-	case 1:
-		dataCenter = options[0]
-	case 2:
-		dataCenter = options[0]
-		rack = options[1]
-	case 3:
-		dataCenter = options[0]
-		rack = options[1]
-		dataNode = options[2]
-	default:
+	if r.DataCenter != "" {
+		values.Add("dataCenter", r.DataCenter)
 	}
-
-	if dataCenter != "" {
-		values.Add("dataCenter", dataCenter)
+	if r.Rack != "" {
+		values.Add("rack", r.Rack)
 	}
-	if rack != "" {
-		values.Add("rack", rack)
-	}
-	if dataNode != "" {
-		values.Add("dataNode", dataNode)
+	if r.DataNode != "" {
+		values.Add("dataNode", r.DataNode)
 	}
 
 	jsonBlob, err := util.Post("http://"+server+"/dir/assign", values)
diff --git a/weed/operation/submit.go b/weed/operation/submit.go
index 19bbd7a70..54b6e164e 100644
--- a/weed/operation/submit.go
+++ b/weed/operation/submit.go
@@ -44,7 +44,13 @@ func SubmitFiles(master string, files []FilePart,
 	for index, file := range files {
 		results[index].FileName = file.FileName
 	}
-	ret, err := Assign(master, uint64(len(files)), replication, collection, ttl)
+	ar := &VolumeAssignRequest{
+		Count:       uint64(len(files)),
+		Replication: replication,
+		Collection:  collection,
+		Ttl:         ttl,
+	}
+	ret, err := Assign(master, ar)
 	if err != nil {
 		for index, _ := range files {
 			results[index].Error = err.Error()
@@ -164,7 +170,13 @@ func (fi FilePart) Upload(maxMB int, master string, secret security.Secret) (ret
 func upload_one_chunk(filename string, reader io.Reader, master,
 	replication string, collection string, ttl string, jwt security.EncodedJwt,
 ) (fid string, size uint32, e error) {
-	ret, err := Assign(master, 1, replication, collection, ttl)
+	ar := &VolumeAssignRequest{
+		Count:       1,
+		Replication: replication,
+		Collection:  collection,
+		Ttl:         ttl,
+	}
+	ret, err := Assign(master, ar)
 	if err != nil {
 		return "", 0, err
 	}
diff --git a/weed/server/common.go b/weed/server/common.go
index 312bcea14..dcd31f823 100644
--- a/weed/server/common.go
+++ b/weed/server/common.go
@@ -94,7 +94,13 @@ func submitForClientHandler(w http.ResponseWriter, r *http.Request, masterUrl st
 
 	debug("assigning file id for", fname)
 	r.ParseForm()
-	assignResult, ae := operation.Assign(masterUrl, 1, r.FormValue("replication"), r.FormValue("collection"), r.FormValue("ttl"))
+	ar := &operation.VolumeAssignRequest{
+		Count:       1,
+		Replication: r.FormValue("replication"),
+		Collection:  r.FormValue("collection"),
+		Ttl:         r.FormValue("ttl"),
+	}
+	assignResult, ae := operation.Assign(masterUrl, ar)
 	if ae != nil {
 		writeJsonError(w, r, http.StatusInternalServerError, ae)
 		return
diff --git a/weed/server/filer_server_handlers_write.go b/weed/server/filer_server_handlers_write.go
index 597004f7d..e2d40f532 100644
--- a/weed/server/filer_server_handlers_write.go
+++ b/weed/server/filer_server_handlers_write.go
@@ -87,7 +87,13 @@ func (fs *FilerServer) queryFileInfoByPath(w http.ResponseWriter, r *http.Reques
 }
 
 func (fs *FilerServer) assignNewFileInfo(w http.ResponseWriter, r *http.Request, replication, collection string) (fileId, urlLocation string, err error) {
-	assignResult, ae := operation.Assign(fs.getMasterNode(), 1, replication, collection, r.URL.Query().Get("ttl"))
+	ar := &operation.VolumeAssignRequest{
+		Count:       1,
+		Replication: replication,
+		Collection:  collection,
+		Ttl:         r.URL.Query().Get("ttl"),
+	}
+	assignResult, ae := operation.Assign(fs.getMasterNode(), ar)
 	if ae != nil {
 		glog.V(0).Infoln("failing to assign a file id", ae.Error())
 		writeJsonError(w, r, http.StatusInternalServerError, ae)