add other replica locations when assigning volumes

weed/server/master_grpc_server_volume.go

@@ -150,12 +150,20 @@ func (ms *MasterServer) Assign(ctx context.Context, req *master_pb.AssignRequest
 		fid, count, dnList, err := ms.Topo.PickForWrite(req.Count, option)
 		if err == nil {
 			dn := dnList.Head()
+			var replicas []*master_pb.AssignResponse_Replica
+			for _, r := range dnList.Rest() {
+				replicas = append(replicas, &master_pb.AssignResponse_Replica{
+					Url:       r.Url(),
+					PublicUrl: r.PublicUrl,
+				})
+			}
 			return &master_pb.AssignResponse{
 				Fid:       fid,
 				Url:       dn.Url(),
 				PublicUrl: dn.PublicUrl,
 				Count:     count,
 				Auth:      string(security.GenJwt(ms.guard.SigningKey, ms.guard.ExpiresAfterSec, fid)),
+				Replicas:  replicas,
 			}, nil
 		}
 		//glog.V(4).Infoln("waiting for volume growing...")