Data difficult to be written to a target sector (write) of a hard disk is recorded to a MRAM. The target sector (write) to which the write has been difficult is checked in a background of performing data write to the next target sector (write). When there is no error, the data stored in the MRAM is written to the target sector (write) of the hard disk. When there is any error, the data stored in the MRAM is written to an alternative sector of the hard disk. Data difficult to be read from a target sector (read) of the hard disk is recorded to the MRAM. The target sector (read) from which the read has been difficult is checked in a background of performing data read from the next target sector (read). When there is any error, the data stored in the MRAM is written to an alternative sector of the hard disk.