diff --git a/weed/server/volume_grpc_copy.go b/weed/server/volume_grpc_copy.go
index 3b6524df8..cf9f9f777 100644
--- a/weed/server/volume_grpc_copy.go
+++ b/weed/server/volume_grpc_copy.go
@@ -61,7 +61,7 @@ func (vs *VolumeServer) VolumeCopy(ctx context.Context, req *volume_server_pb.Vo
 		}
 		location := vs.store.FindFreeLocation(types.ToDiskType(diskType))
 		if location == nil {
-			return fmt.Errorf("no space left")
+			return fmt.Errorf("no space left for disk type %s", types.ToDiskType(diskType).ReadableString())
 		}
 
 		dataBaseFileName = storage.VolumeFileName(location.Directory, volFileInfoResp.Collection, int(req.VolumeId))
diff --git a/weed/shell/command_volume_tier_move.go b/weed/shell/command_volume_tier_move.go
index fb52c5d96..a15efd6b3 100644
--- a/weed/shell/command_volume_tier_move.go
+++ b/weed/shell/command_volume_tier_move.go
@@ -116,7 +116,7 @@ func doVolumeTierMove(commandEnv *CommandEnv, writer io.Writer, collection strin
 			if sourceVolumeServer == "" {
 				continue
 			}
-			fmt.Fprintf(writer, "moving volume %d %s from %s to dataNode %s with disk type ...\n", vid, sourceVolumeServer, dst.dataNode.Id, toDiskType.String())
+			fmt.Fprintf(writer, "moving volume %d from %s to %s with disk type %s ...\n", vid, sourceVolumeServer, dst.dataNode.Id, toDiskType.ReadableString())
 			hasFoundTarget = true
 
 			if !applyChanges {
@@ -127,7 +127,7 @@ func doVolumeTierMove(commandEnv *CommandEnv, writer io.Writer, collection strin
 			if err = markVolumeReadonly(commandEnv.option.GrpcDialOption, vid, locations); err != nil {
 				return fmt.Errorf("mark volume %d as readonly on %s: %v", vid, locations[0].Url, err)
 			}
-			if err = LiveMoveVolume(commandEnv.option.GrpcDialOption, vid, sourceVolumeServer, dst.dataNode.Id, 5*time.Second, toDiskType.String()); err != nil {
+			if err = LiveMoveVolume(commandEnv.option.GrpcDialOption, vid, sourceVolumeServer, dst.dataNode.Id, 5*time.Second, toDiskType.ReadableString()); err != nil {
 				return fmt.Errorf("move volume %d %s => %s : %v", vid, locations[0].Url, dst.dataNode.Id, err)
 			}
 
@@ -143,7 +143,7 @@ func doVolumeTierMove(commandEnv *CommandEnv, writer io.Writer, collection strin
 	}
 
 	if !hasFoundTarget {
-		fmt.Fprintf(writer, "can not find disk type %s for volume %d\n", toDiskType.String(), vid)
+		fmt.Fprintf(writer, "can not find disk type %s for volume %d\n", toDiskType.ReadableString(), vid)
 	}
 
 	return nil
diff --git a/weed/storage/types/volume_disk_type.go b/weed/storage/types/volume_disk_type.go
index 25056ee10..c9b87d802 100644
--- a/weed/storage/types/volume_disk_type.go
+++ b/weed/storage/types/volume_disk_type.go
@@ -31,3 +31,10 @@ func (diskType DiskType) String() string {
 	}
 	return string(diskType)
 }
+
+func (diskType DiskType) ReadableString() string {
+	if diskType == "" {
+		return "hdd"
+	}
+	return string(diskType)
+}