Magnetic disk device

A magnetic disk device comprising:

• a disk including a first data track and a second data track adjacent to each other in a recording layer, the first data track and the second data track each including a plurality of target sectors being targets to which data is to be written, the first data track being located in a first direction parallel to a radial direction of the disk as viewed from the second data track;
• a head including a write head writing data to the recording layer and a read head reading data from the recording layer;
• a read processing unit capable of executing seek processing of causing the read head to seek;
• a write processing unit capable of executing write processing of writing data to the recording layer;
• an error correction unit executing error correction of data in one or more corrupted target sectors in which data is considered to be corrupted, among the plurality of target sectors of the first data track;
• a buffer memory capable of holding a plurality of elements of data including first user data and second user data;
• a management unit capable of selectively executing first management of prohibiting overwrite to the first user data in the buffer memory, second management of permitting overwrite to all elements of the first user data in the buffer memory, and third management of permitting overwrite to data belonging to a first group and a second group among the first user data in the buffer memory and prohibiting overwrite to data belonging to a third group among the first user data in the buffer memory;
• a correction limit discrimination unit;
• and
• a determination unit,
• wherein
• during a first write period being a period elapsed after the write processing unit executes the write processing of writing first data including the first user data to the plurality of target sectors of the first data track, and the period during which the write processing unit executes the write processing of writing second data including the second user data to the plurality of target sectors of the second data track,
• the read processing unit executes seek processing of causing the read head to seek and makes the write head face the second data track,
• each time data is written to each of the target sectors of the second data track, the correction limit discrimination unit obtains information that a position of the write head is displaced beyond a reference radius position in the first direction, and
• the management unit executes the first management, and
• if determining that the error correction of the first user data on the first data track, which is executed by the error correction unit, does not exceed a limit, based on the information obtained by the correction limit discrimination unit, the determination unit causes the write processing unit to continue the write processing for the second data track and causes the management unit to execute the second management instead of the first management, and
• if determining that the error correction of the first user data on the first data track, which is executed by the error correction unit, exceeds the limit, based on the information, the determination unit causes the write processing unit to continue the write processing for the second data track and causes the management unit to execute the third management instead of the first management, and
• during the first write period or after the first write period,
• the determination unit causes the management unit to execute processing of saving data belonging to the third group to a nonvolatile recording medium,
• the data belonging to the first group is original data of the data of one or more target sectors in which the data is determined to be uncorrupted, among the plurality of target sectors of the first data track,
• the data belonging to the second group is original data of the data of one or more first corrupted target sectors in which the data is determined to be corrupted, among the plurality of target sectors of the first data track, and original data of the data within a range of being subjected to the error correction executed by the error correction unit, and
• the data belonging to the third group is original data of the data of one or more second corrupted target sectors in which the data is determined to be corrupted, among the plurality of target sectors of the first data track, and original data of the data which leaks from the range of being subjected to the error correction executed by the error correction unit.