In a controller of a tape drive, a CM input-output unit recognizes a tape format; a tape variable acquisition unit acquires tape variables; a setting variable acquisition unit acquires setting variables; and a minimum number calculator calculates a minimum number m of sub datasets, which are to be written to a tape to secure resistance to burst error, by using the tape variables and setting variables. When a command processor receives a synchronization command, the buffer manager generates n sub datasets for storing data in the buffer. If n is smaller than m, m sub datasets are padded out and set as write data. If n is m or more, the n sub datasets are set as write data. Then, the channel input-output unit writes the write data to the tape.