Magnetic disk device and control method
A magnetic disk device is a magnetic disk device in which data write is performed by a thermal assist method, the magnetic disk device including: a magnetic disk that includes a plurality of tracks; and a controller that controls the magnetic disk device, wherein the controller measures, every a first period, a deviation amount from a reference height of a surface of the magnetic disk with respect to a track in which a duty ratio is equal to or greater than a predetermined value, the duty ratio being a time ratio at which data write is performed per unit time, among the plurality of tracks, and flattens the surface of the magnetic disk in a case where the deviation amount becomes equal to or greater than a first value.
1 . A magnetic disk device in which data write is performed by a thermal assist method, the magnetic disk device comprising:
a magnetic disk that includes a plurality of tracks; and
a controller that controls the magnetic disk device, wherein
the controller
measures, every first period, a deviation amount from a reference height of a surface of the magnetic disk with respect to a track in which a duty ratio is equal to or greater than a predetermined value, the duty ratio being a time ratio at which data write is performed per unit time, among the plurality of tracks, and
flattens the surface of the magnetic disk in a case where the deviation amount becomes equal to or greater than a first value.
2 . The magnetic disk device according to claim 1 , wherein
the controller ends measurement of the deviation amount when the deviation amount becomes equal to or less than a second value smaller than a value at start of the measurement in a case where the deviation amount is measured every first period.
3 . The magnetic disk device according to claim 2 , wherein
the controller flattens the surface when the deviation amount does not reach the first value or more or does not reach the second value or less, and a number of times of measurement reaches a first number of times in a case where the deviation amount is measured every first period.
4 . The magnetic disk device according to claim 1 , further comprising:
a magnetic head that performs data write on the magnetic disk, wherein
the magnetic head includes a resistance type temperature sensor, and
the controller measures the deviation amount from a first result obtained by sensing the surface of the magnetic disk by the resistance type temperature sensor.
5 . The magnetic disk device according to claim 4 , wherein
the controller
acquires in advance a second result obtained by sensing the surface of the magnetic disk in an initial state with the resistance type temperature sensor for each of the plurality of tracks or for each of a plurality of zones grouped for a predetermined number of tracks among the plurality of tracks, and
sets the second result as the reference height for each of the plurality of tracks or for each of the plurality of zones, and estimates the deviation amount from a difference between the first result and the second result.
6 . The magnetic disk device according to claim 5 , wherein
the controller
in a case where the second result is acquired for each of the plurality of tracks, estimates the deviation amount based on a difference between the first result and the second result for a track in which the duty ratio is equal to or greater than the predetermined value, and
in a case where the second result is acquired for each of the plurality of zones, estimates the deviation amount based on a difference between the first result for a track in which the duty ratio is equal to or greater than the predetermined value and the second result for a zone to which the track in which the duty ratio is equal to or greater than the predetermined value belongs among the plurality of zones.
7 . The magnetic disk device according to claim 5 , wherein
the magnetic head includes first and second heaters that are provided to be spaced apart from each other in the magnetic head in a direction along the magnetic disk, and are capable of adjusting a flying amount of the magnetic head that is a distance of the magnetic head from the magnetic disk by thermally expanding the magnetic head, and
when acquiring the first and second results with the resistance type temperature sensor, the controller supplies electric power to the first and second heaters at a predetermined ratio to adjust the flying amount of the magnetic head.
8 . The magnetic disk device according to claim 7 , wherein
the controller
forms a pseudo deviation of the surface of the magnetic disk in the initial state from the reference height,
measures the pseudo deviation by supplying different electric power to the first and second heaters at different ratios to make the flying amount of the magnetic head different, and
based on a result of measuring the pseudo deviation, determines in advance an appropriate value of the flying amount of the magnetic head when acquiring the first and second results with the resistance type temperature sensor.
9 . The magnetic disk device according to claim 1 , further comprising:
an assist mechanism that heats the magnetic disk, wherein
the controller flattens the surface of the magnetic disk by supplying assist power to the assist mechanism and heating a corresponding portion of the track at a temperature lower than a temperature at time of data write.
10 . The magnetic disk device according to claim 9 , wherein
the magnetic disk includes
a substrate,
a recording layer that is provided on the substrate, and
a lubricant that covers the recording layer.
11 . The magnetic disk device according to claim 9 , wherein
the controller
forms a pseudo deviation of the surface of the magnetic disk in the initial state from the reference height,
determines in advance an appropriate value of the assist power to be supplied to the assist mechanism when flattening the surface of the magnetic disk based on an elimination speed of the pseudo deviation while supplying different assist power to the assist mechanism and heating the surface of the magnetic disk, and
supplies the assist power based on the appropriate value to the assist mechanism when flattening the surface.
12 . The magnetic disk device according to claim 11 , further comprising
a magnetic head that performs data write on the magnetic disk, wherein
the assist mechanism is provided in the magnetic head, and
when determining the appropriate value of the assist power, the controller determines an appropriate value of a flying amount of the magnetic head that is a distance of the magnetic head from the magnetic disk at time of flattening the surface, and
supplies the assist power based on the appropriate value of the assist power to the assist mechanism while controlling the magnetic head with the flying amount based on the appropriate value of the flying amount when flattening the surface.
13 . The magnetic disk device according to claim 12 , wherein
the magnetic head includes first and second heaters that are provided to be spaced apart from each other in the magnetic head in a direction along the magnetic disk, and are capable of adjusting the flying amount by thermally expanding the magnetic head, and
when determining the appropriate value of the flying amount, the controller determines the appropriate value of the flying amount when flattening the surface based on a result of varying an electric power value and an electric power ratio and supplying electric power to each of the first and second heaters to change the flying amount of the magnetic head.
14 . The magnetic disk device according to claim 1 , wherein
the controller
measures, every second period, a deviation amount from a reference height of a surface of the magnetic disk with respect to one or more tracks adjacent to the track in which the duty ratio is equal to or greater than the predetermined value in addition to the track, and
flattens the surface of the one or more tracks in a case where the deviation amount of the one or more tracks becomes equal to or greater than a third value.
15 . The magnetic disk device according to claim 14 , wherein
the controller ends measurement of the one or more tracks when the deviation amount becomes equal to or less than a fourth value smaller than a value at start of the measurement in a case where the deviation amount is measured every second period.
16 . The magnetic disk device according to claim 15 , wherein
the controller flattens the surface when the deviation amount does not reach the third value or more or does not reach the fourth value or less, and a number of times of measurement reaches a second number of times in a case where the deviation amount is measured every second period.
17 . A control method executed in a magnetic disk device in which data write is performed by a thermal assist method, the control method comprising:
measuring, every first period, a deviation amount from a reference height of a surface of a magnetic disk with respect to a track in which a duty ratio is equal to or greater than a predetermined value, the duty ratio being a time ratio at which data write is performed per unit time, among a plurality of tracks included in the magnetic disk; and
flattening the surface of the magnetic disk in a case where the deviation amount becomes equal to or greater than a first value.