Magnetic disk apparatus and method

A magnetic disk apparatus comprising:

• a magnetic disk including tracks on which multiple servo sectors storing servo information are arranged at intervals in a circumferential direction, the multiple servo sectors including a first track and a second track adjacent to the first track in a radial direction, the second track being subjected to writing before the first track is, the first track and the second track each including data sectors, the data sectors including a data sector in which an error correction code is stored to perform error correction on the corresponding first or second track;
• a magnetic head configured to write data and read data to and from the magnetic disk;
• and
• a controller configured to
• read servo information when the magnetic head passes over each of the multiple servo sectors and execute, based on the read servo information, a write operation on the first track while executing positioning of the magnetic head on the first track,
• execute, during the write operation, a determination operation when the magnetic head passes over a first servo sector being one of the multiple servo sectors, the determination operation being executed by:
• calculating a first cumulative amount obtained by accumulating, for a first section, evaluation amounts each corresponding to an amount by which a width of the second track is narrowed due to the write operation, and determining whether the first cumulative amount is smaller or larger than a first threshold value corresponding to a correction limit of the error correction, the first section including a second section and a third section, the second section being a section in which writing of data in a circumferential direction of the first track is completed, the third section being a section in which data is written subsequent to the second section in the circumferential direction of the first track,
• interrupt the write operation in response to determining, by the determination operation, that the first cumulative amount is larger than the first threshold value,
• execute, after the write operation is interrupted, a rotational delay of the magnetic disk and re-execute the determination operation when the magnetic head passes over the first servo sector again, and
• resume the write operation in response to determining, by the re-executed determination operation, that the first cumulative amount is smaller than the first threshold value.