Magnetic disk device

A magnetic disk device comprising:

• a disk including a user data area including a first data track and a second data track continuous in a radial direction, in a recording layer, the first data track and the second data track each including a plurality of target sectors as targets to which data is written;
• a write head writing data to the recording layer of the disk;
• a volatile buffer memory;
• a parity generation unit;
• 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 of a corrupted target sector in which data is determined to be corrupted among the plurality of target sectors of each of the first data track and the second data track;
• a storage processing unit;
• and
• a conventional correction limit prediction unit,
• wherein
• the write processing unit writes first user data to the plurality of target sectors of the first data track and uses the target sectors as a plurality of user data sectors, during a first write period,
• the write processing unit writes second user data to the plurality of target sectors of the second data track and uses the target sectors as a plurality of user data sectors, during a second write period following the first write period,
• the parity generation unit generates first conventional parity and first potential parity for error correction of first corrupted data of one or more corrupted target sectors of the first data track, based on the first user data,
• an ability of the first potential parity to execute error correction of the first corrupted data is higher than an ability of the first conventional parity to execute error correction of the first corrupted data,
• the parity generation unit generates second conventional parity and second potential parity for error correction of second corrupted data of one or more corrupted target sectors of the second data track, based on the second user data,
• an ability of the second potential parity to execute error correction of the second corrupted data is higher than an ability of the second conventional parity to execute error correction of the second corrupted data,
• the storage processing unit stores the first potential parity in the buffer memory, and then stores the second potential parity in the buffer memory,
• the conventional correction limit prediction unit generates first prediction information that is the information for predicting whether the first conventional error correction of the first corrupted data, which is executed using the first conventional parity by the error correction unit, reaches its limit after the second user data is written to the second data track,
• if the first prediction information is normal information for predicting that the first conventional error correction does not reach its limit, the storage processing unit maintains a recording area where the potential parity is stored, in the buffer memory, stores the second potential parity in the first recording area where the first potential parity is stored, in the buffer memory, and overwrites the second potential parity to the first recording area, and
• if the first prediction information is replaced with abnormal information for predicting that the first conventional error correction reaches its limit, the storage processing unit changes the recording area where the potential parity is stored, in the buffer memory, leaves the first potential parity in the first recording area, and stores the second potential parity in the second recording area which is different from the first recording area, in the buffer memory.