assign fileId according to DataNode with empty DataCenter and Rack

weed/topology/volume_layout.go

@@ -281,7 +281,7 @@ func (vl *VolumeLayout) PickForWrite(count uint64, option *VolumeGrowOption) (*n
 		//glog.V(0).Infoln("No more writable volumes!")
 		return nil, 0, nil, errors.New("No more writable volumes!")
 	}
-	if option.DataCenter == "" {
+	if option.DataCenter == "" && option.Rack == "" && option.DataNode == "" {
 		vid := vl.writables[rand.Intn(lenWriters)]
 		locationList := vl.vid2location[vid]
 		if locationList != nil {
@@ -295,7 +295,9 @@ func (vl *VolumeLayout) PickForWrite(count uint64, option *VolumeGrowOption) (*n
 	for _, v := range vl.writables {
 		volumeLocationList := vl.vid2location[v]
 		for _, dn := range volumeLocationList.list {
-			if dn.GetDataCenter().Id() == NodeId(option.DataCenter) {
+			if option.DataCenter != "" && dn.GetDataCenter().Id() != NodeId(option.DataCenter) {
+				continue
+			}
 			if option.Rack != "" && dn.GetRack().Id() != NodeId(option.Rack) {
 				continue
 			}
@@ -308,7 +310,6 @@ func (vl *VolumeLayout) PickForWrite(count uint64, option *VolumeGrowOption) (*n
 			}
 		}
 	}
-	}
 	return &vid, count, locationList, nil
 }