A mechanism is provided for updating data of a file on a tape in a file system using a tape drive. Data of a file which received a write request is read out from a tape drive and stored in a memory. At least a part of the data of the file is edited and the edited data part of the file is stored in the memory. Combination data with a non-edited data part and the edited data part of the file is written on the tape in the tape drive as a continuous data of the file to have an extent. The extent of the written continuous data of the file is then written on the tape.