Magnetic disk drive using offset in positioning head to read data and head positioning method
According to one embodiment, a magnetic disk drive comprises a write count memory, a read offset setting module and a controller. The write count memory stores a write count for each track or for each zone on a disk. The read offset setting module sets, in accordance with a write count for an adjacent track to a target track or for a zone to which the adjacent track belongs, an offset from a predetermined position on the target track in a read position in which a head is to be positioned when the head is positioned on the target track for data read. The write count is stored in the write count memory. The controller positions the head in a position shifted from the predetermined position by the set offset.
1. A magnetic disk drive comprising:
a write count memory configured to store a write count for each track or for each zone on a disk;
a table in which a result of measuring an erase width corresponding to the write count for each track or for each zone has been stored as a read offset parameter value, the read offset parameter value being used to determine an offset from a predetermined position on a target track in a read position in which a head is to be positioned, the result of measuring the erase width including a first erase width E(+) in an inner direction of the disk and a second erase width E(−) in an outer direction of the disk, the first erase width E(+) and the second erase width E(−) both using the predetermined position in the corresponding track or each track belonging to the corresponding zone as a reference;
a table access module configured to obtain a first erase width E(+) corresponding to a first write count stored in the write count memory and a second erase width E(−) corresponding to a second write count stored in the write count memory by accessing the table in accordance with the first write count and the second write count when the head is positioned on the target track for data read, the first write count being a write count for an outer adjacent track or for a zone to which the outer adjacent track belongs and the second write count being a write count for an inner adjacent track or for a zone to which the inner adjacent track belongs, the outer adjacent track being adjacent to the target track on an outer diameter zone of the disk and the inner adjacent track being adjacent to the target track on an inner diameter zone of the disk;
a read offset setting module configured to set the offset based on the obtained first erase width E(+) and second erase width E(−); and
a controller configured to position the head in a position shifted from the predetermined position by the set offset.
2. The magnetic disk drive of claim 1 , wherein the read offset setting module is further configured to determine the offset by calculating (E(+)−E(−))/2.
3. The magnetic disk drive of claim 2 , wherein the table access module is further configured to interpolate, based on the table, the first erase width E(+) corresponding to the first write count or the second erase width E(−) corresponding to the second write count if the first erase width E(+) or the second erase width E(−) has not been stored in the table.
4. The magnetic disk drive of claim 2 , wherein the table access module is further configured:
to obtain, as the first erase width E(+) from the table, an erase width E(+) corresponding to a first track or a first zone for which a write count is closest to the first write count if the first erase width E(+) corresponding to the first write count has not been stored in the table; and
to obtain, as the second erase width E(−) from the table, an erase width E(−) corresponding to a second track or a second zone for which a write count is closest to the second write count if the second erase width E(−) corresponding to the second write count has not been stored in the table.
5. A method of positioning a head on a target track in a magnetic disk drive which comprises a write count memory which stores a write count for each track or for each zone on a disk and a table in which a result of measuring an erase width corresponding to the write count for each track or for each zone has been stored as a read offset parameter value, the read offset parameter value being used to determine an offset from a predetermined position on a target track in a read position in which a head is to be positioned, the result of measuring the erase width including a first erase width E(+) in an inner direction of the disk and a second erase width E(−) in an outer direction of the disk, the first erase width E(+) and the second erase width E(−) both using the predetermined position in the corresponding track or each track belonging to the corresponding zone as a reference, the method comprising:
obtaining a first write count and a second write count stored in the write count memory when the head is positioned on the target track for data read, the first write count being a write count for an outer adjacent track or for a zone to which the outer adjacent track belongs and the second write count being a write count for an inner adjacent track or for a zone to which the inner adjacent track belongs, the outer adjacent track being adjacent to the target track on an outer diameter zone of the disk and the inner adjacent track being adjacent to the target track on an inner diameter zone of the disk;
obtaining a first erase width E(+) corresponding to the first write count and a second erase width E(−) corresponding to the second write count by accessing the table;
setting the offset based on the obtained first erase width E(+) and second erase width E(−); and
positioning the head in a position shifted from the predetermined position by the set offset.
6. The method of claim 5 , further comprising determining the offset by calculating (E(+)−E(−))/2.
7. The method of claim 6 , further comprising interpolating, based on the table, the first erase width E(+) corresponding to the first write count or the second erase width E(−) corresponding to the second write count if the first erase width E(+) or the second erase width E(−) has not been stored in the table.
8. The method of claim 6 , further comprising:
obtaining, as the first erase width E(+) from the table, an erase width E(+) corresponding to a first track or a first zone for which a write count is closest to the first write count if the first erase width E(+) corresponding to the first write count has not been stored in the table; and
obtaining, as the second erase width E(−) from the table, an erase width E(−) corresponding to a second track or a second zone for which a write count is closest to the second write count if the second erase width E(−) corresponding to the second write count has not been stored in the table.