Dynamic track pitch control for shingled magnetic recording (SMR)
View Patent ↗SMR disk drives are described that adjust track pitch or magnetic write width to compensate for external temperature effects. In one embodiment track pitch is increased when the media temperature increases. The temperature of magnetic media during write operations can be determined from the drives' temperature sensor. In other embodiments track pitch is adjusted based on the magnetic write width (MWW) which is determined from read-back testing of previously written data tracks. In an alternative embodiment, the width of the MWW is adjusted instead of the track pitch. The various factors that affect the MWW that can be used to increase or decrease the MWW, including write current characteristics and when available thermal-assistance parameters.
1. A method of operating a Shingled Magnetic Recording disk drive comprising:
measuring a selected temperature in the disk drive, the selected temperature representing thin film magnetic media temperature on a disk; and
selecting a track pitch for a next shingled write operation on the disk using the selected temperature, the selected track pitch being a positive function of the selected temperature that increases to a maximum track pitch corresponding to a maximum temperature and decreases to a minimum track pitch corresponding to a minimum temperature, the selected track pitch resulting in a partial overlapping of a previously written track by the next shingled write operation.
2. The method of claim 1 wherein a magnetic write width for the write operation varies with values of the selected temperature and the selected track pitch compensates at least in part for increases in the magnetic write width by increasing the selected track pitch for higher temperatures and decreasing the selected track pitch for lower temperatures.
3. The method of claim 2 wherein a first value of the selected temperature corresponds to a first magnetic write width and a second value of the selected temperature higher than the first value corresponds to a second magnetic write width higher than the first magnetic write width and selecting a track pitch for the second value of the selected temperature that higher than the track pitch for the first value by an amount approximately equal to one half of the difference between the first and second magnetic write widths.
4. A method of operating a Shingled Magnetic Recording disk drive comprising:
measuring a current magnetic write width by performing test writes and reads in the thin film magnetic media on a disk; and
selecting a track pitch for a next shingled write operation, the track pitch being a positive function of the current magnetic write width that compensates for increases in the current magnetic write width by increasing the track pitch up to a maximum track pitch that is selected for a maximum current magnetic write width and compensates for decreases in the current magnetic write width by decreasing the track pitch to a minimum track pitch that is selected for a minimum current magnetic write width, wherein the selected track pitch compensates for changes in the current magnetic write width.
5. The method of claim 4 wherein selecting a track pitch further comprises mapping changes in the current magnetic write width to changes in the selected track pitch so that the track pitch changes by an amount approximately equal to one half of the change in current magnetic write width.
6. A method of operating a Shingled Magnetic Recording disk drive comprising:
measuring a current magnetic write width by performing test writes and reads in the thin film magnetic media on a disk using a first set of writing parameters; and
adjusting the current magnetic write width to conform to a predetermined value by adjusting one or more writing parameters.
7. The method of claim 6 wherein adjusting the magnetic write width further comprises changing a write current parameter to increase or decrease the magnetic write width.
8. The method of claim 6 wherein adjusting the magnetic write width further comprises changing a thermal assist parameter to increase or decrease the temperature of the film magnetic media.
9. The method of claim 6 wherein adjusting the magnetic write width further comprises changing an overshoot current to increase or decrease the film magnetic write width.
10. A Shingled Magnetic Recording disk drive comprising:
temperature sensor for measuring a selected temperature representing magnetic media temperature on a disk; and
a track pitch adjustment unit that adjust the track pitch by selecting a track pitch value for a next write operation using the selected temperature, the selected track pitch value being a positive function of the selected temperature up to a maximum track pitch value that is selected for a maximum temperature and wherein a minimum track pitch value is selected for a minimum temperature, and the selected track pitch value results in a partial overlapping of a previously written track by the next write operation.
11. The Shingled Magnetic Recording disk drive of claim 10 wherein a magnetic write width for the write operation increases with the selected temperature and the track pitch adjustment unit adjusts for increases in magnetic write width by increasing the track pitch value.
12. The Shingled Magnetic Recording disk drive of claim 10 wherein the selected track pitch value is a function of the selected temperature so that the track pitch value increases with temperature by an amount approximately equal to one half of an increase in magnetic write width for first and second values of the selected temperature where the second value is higher than the first value.
13. A Shingled Magnetic Recording disk drive comprising:
magnetic media on a disk organized into at least one unshingled region and one shingled region; and
a track pitch adjustment unit that adjusts the track pitch by selecting a track pitch value for a next shingled write operation in the shingled region using a measured magnetic write width value determined by writing and reading test data in the magnetic media, the selected track pitch value being a positive function of the measured magnetic write width value up to a maximum track pitch that is selected for a maximum measured magnetic write width value and where a minimum track pitch is selected for a minimum measured magnetic write width, wherein the selected track pitch value compensates at least in part for changes in the magnetic write width value.
14. The Shingled Magnetic Recording disk drive of claim 13 wherein the selected track pitch value increases with magnetic write width values by an amount approximately equal to one half of an increase in magnetic write width for first and second values of the magnetic write width where the second value is higher than the first value.
15. A Shingled Magnetic Recording disk drive comprising:
magnetic media on a disk organized into at least one unshingled region and one shingled region; and
a magnetic write width adjustment unit that adjusts the magnetic write width by selecting write parameters for a next shingled write operation in the shingled region by measuring a first magnetic write width value determined by writing and reading test data in the magnetic media using a first set of write parameters, and then selecting a second set of write parameters to adjust the magnetic write width value to correspond to a predetermined target value.