add disable volume_growth flag (#7196)

weed/server/master_server_handlers.go

@@ -142,7 +142,7 @@ func (ms *MasterServer) dirAssignHandler(w http.ResponseWriter, r *http.Request)
 
 	for time.Since(startTime) < maxTimeout {
 		fid, count, dnList, shouldGrow, err := ms.Topo.PickForWrite(requestedCount, option, vl)
-		if shouldGrow && !vl.HasGrowRequest() {
+		if shouldGrow && !vl.HasGrowRequest() && !ms.option.VolumeGrowthDisabled {
 			glog.V(0).Infof("dirAssign volume growth %v from %v", option.String(), r.RemoteAddr)
 			if err != nil && ms.Topo.AvailableSpaceFor(option) <= 0 {
 				err = fmt.Errorf("%s and no free volumes left for %s", err.Error(), option.String())