Embodiments in accordance with the present invention relate to detecting a
micro-relief that exists on surfaces of a magnetic disk. A phase or
frequency of a read signal obtained when data written to a minute
projection or a minute concavity on a recording surface of a magnetic
disk is read out, differs from that of a read signal obtained when data
written to a flat recording surface is read out. The phase progresses in
the minute projection, whereas the phase is delayed in the minute
concavity. A micro-relief is detected by measuring a deviation value of
this frequency, and then defect registration is performed. Embodiments in
accordance with the present invention are configured to detect a minute
projection whose level does not cause TA. Embodiments in accordance with
the present invention may also be configured to provide a highly reliable
magnetic disk drive by controlling the flying height in response to a
state of a minute projection and that of a minute concavity.