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.