volume copying adds cleaning up on error

fix https://github.com/chrislusf/seaweedfs/issues/1253

weed/server/volume_grpc_copy.go

@@ -25,7 +25,20 @@ func (vs *VolumeServer) VolumeCopy(ctx context.Context, req *volume_server_pb.Vo
 
 	v := vs.store.GetVolume(needle.VolumeId(req.VolumeId))
 	if v != nil {
-		return nil, fmt.Errorf("volume %d already exists", req.VolumeId)
+
+		glog.V(0).Infof("volume %d already exists. deleted before copying...", req.VolumeId)
+
+		err := vs.store.UnmountVolume(needle.VolumeId(req.VolumeId))
+		if err != nil {
+			return nil, fmt.Errorf("failed to mount existing volume %d: %v", req.VolumeId, err)
+		}
+
+		err = vs.store.DeleteVolume(needle.VolumeId(req.VolumeId))
+		if err != nil {
+			return nil, fmt.Errorf("failed to delete existing volume %d: %v", req.VolumeId, err)
+		}
+
+		glog.V(0).Infof("deleted exisitng volume %d before copying.", req.VolumeId)
 	}
 
 	location := vs.store.FindFreeLocation()
@@ -73,10 +86,15 @@ func (vs *VolumeServer) VolumeCopy(ctx context.Context, req *volume_server_pb.Vo
 	idxFileName = volumeFileName + ".idx"
 	datFileName = volumeFileName + ".dat"
 
+	defer func() {
 		if err != nil && volumeFileName != "" {
 			os.Remove(idxFileName)
 			os.Remove(datFileName)
 			os.Remove(volumeFileName + ".vif")
+		}
+	}()
+
+	if err != nil && volumeFileName != "" {
 		return nil, err
 	}