The data storage system 1 comprises tape drives 21 to 23 operable to read and write data transmitted via the SCSI bus 112 from and on a tape in parallel and a host PC 4 for controlling data transmission to the SCSI bus. The host PC 4 includes a data access control unit 41 operable to calculate a bus reconnect timing that makes it possible to avoid stopping tape writing or reading even when any one of the respective drive drives 21 to 23 waits for the time when the other tape drives finish data transmitting after it reaches a bus reconnect timing based on the tape drive information "(the number of drive units, a data transmission speed of the bus, either a data reading speeds of the respective drive units or a data writing speeds of the respective drive units)=(m, S and R)".