diff --git a/weed/command/webdav.go b/weed/command/webdav.go
index 9ab2ce9de..125893dfa 100644
--- a/weed/command/webdav.go
+++ b/weed/command/webdav.go
@@ -37,7 +37,7 @@ func init() {
 
 var cmdWebDav = &Command{
 	UsageLine: "webdav -port=7333 -filer=<ip:port>",
-	Short:     "start a webdav server that is backed by a filer",
+	Short:     "<unstable> start a webdav server that is backed by a filer",
 	Long: `start a webdav server that is backed by a filer.
 
 `,
diff --git a/weed/pb/volume_server.proto b/weed/pb/volume_server.proto
index ec4f09ef1..b5ebe6bed 100644
--- a/weed/pb/volume_server.proto
+++ b/weed/pb/volume_server.proto
@@ -162,10 +162,9 @@ message VolumeCopyResponse {
 
 message CopyFileRequest {
     uint32 volume_id = 1;
-    bool is_idx_file = 2;
-    bool is_dat_file = 3;
-    uint32 compaction_revision = 4;
-    uint64 stop_offset = 5;
+    string ext = 2;
+    uint32 compaction_revision = 3;
+    uint64 stop_offset = 4;
 }
 message CopyFileResponse {
     bytes file_content = 1;
diff --git a/weed/pb/volume_server_pb/volume_server.pb.go b/weed/pb/volume_server_pb/volume_server.pb.go
index 30419967b..10bebc65e 100644
--- a/weed/pb/volume_server_pb/volume_server.pb.go
+++ b/weed/pb/volume_server_pb/volume_server.pb.go
@@ -600,10 +600,9 @@ func (m *VolumeCopyResponse) GetLastAppendAtNs() uint64 {
 
 type CopyFileRequest struct {
 	VolumeId           uint32 `protobuf:"varint,1,opt,name=volume_id,json=volumeId" json:"volume_id,omitempty"`
-	IsIdxFile          bool   `protobuf:"varint,2,opt,name=is_idx_file,json=isIdxFile" json:"is_idx_file,omitempty"`
-	IsDatFile          bool   `protobuf:"varint,3,opt,name=is_dat_file,json=isDatFile" json:"is_dat_file,omitempty"`
-	CompactionRevision uint32 `protobuf:"varint,4,opt,name=compaction_revision,json=compactionRevision" json:"compaction_revision,omitempty"`
-	StopOffset         uint64 `protobuf:"varint,5,opt,name=stop_offset,json=stopOffset" json:"stop_offset,omitempty"`
+	Ext                string `protobuf:"bytes,2,opt,name=ext" json:"ext,omitempty"`
+	CompactionRevision uint32 `protobuf:"varint,3,opt,name=compaction_revision,json=compactionRevision" json:"compaction_revision,omitempty"`
+	StopOffset         uint64 `protobuf:"varint,4,opt,name=stop_offset,json=stopOffset" json:"stop_offset,omitempty"`
 }
 
 func (m *CopyFileRequest) Reset()                    { *m = CopyFileRequest{} }
@@ -618,18 +617,11 @@ func (m *CopyFileRequest) GetVolumeId() uint32 {
 	return 0
 }
 
-func (m *CopyFileRequest) GetIsIdxFile() bool {
+func (m *CopyFileRequest) GetExt() string {
 	if m != nil {
-		return m.IsIdxFile
+		return m.Ext
 	}
-	return false
-}
-
-func (m *CopyFileRequest) GetIsDatFile() bool {
-	if m != nil {
-		return m.IsDatFile
-	}
-	return false
+	return ""
 }
 
 func (m *CopyFileRequest) GetCompactionRevision() uint32 {
@@ -1696,96 +1688,95 @@ var _VolumeServer_serviceDesc = grpc.ServiceDesc{
 func init() { proto.RegisterFile("volume_server.proto", fileDescriptor0) }
 
 var fileDescriptor0 = []byte{
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+	0x00, 0x00, 0xff, 0xff, 0x5d, 0xbf, 0x08, 0x06, 0x1e, 0x14, 0x00, 0x00,
 }
diff --git a/weed/server/volume_grpc_copy.go b/weed/server/volume_grpc_copy.go
index e3ade61a1..6bb61dfba 100644
--- a/weed/server/volume_grpc_copy.go
+++ b/weed/server/volume_grpc_copy.go
@@ -52,7 +52,7 @@ func (vs *VolumeServer) VolumeCopy(ctx context.Context, req *volume_server_pb.Vo
 
 		copyFileClient, err := client.CopyFile(ctx, &volume_server_pb.CopyFileRequest{
 			VolumeId:           req.VolumeId,
-			IsIdxFile:          true,
+			Ext:                ".idx",
 			CompactionRevision: volFileInfoResp.CompactionRevision,
 			StopOffset:         volFileInfoResp.IdxFileSize,
 		})
@@ -68,7 +68,7 @@ func (vs *VolumeServer) VolumeCopy(ctx context.Context, req *volume_server_pb.Vo
 
 		copyFileClient, err = client.CopyFile(ctx, &volume_server_pb.CopyFileRequest{
 			VolumeId:           req.VolumeId,
-			IsDatFile:          true,
+			Ext:                ".dat",
 			CompactionRevision: volFileInfoResp.CompactionRevision,
 			StopOffset:         volFileInfoResp.DatFileSize,
 		})
@@ -189,12 +189,7 @@ func (vs *VolumeServer) CopyFile(req *volume_server_pb.CopyFileRequest, stream v
 	bytesToRead := int64(req.StopOffset)
 
 	const BufferSize = 1024 * 1024 * 2
-	var fileName = v.FileName()
-	if req.IsDatFile {
-		fileName += ".dat"
-	} else if req.IsIdxFile {
-		fileName += ".idx"
-	}
+	var fileName = v.FileName() + req.Ext
 	file, err := os.Open(fileName)
 	if err != nil {
 		return err