Magnetic disk apparatus and method

A method of controlling a magnetic disk apparatus, the magnetic disk apparatus including a magnetic disk and a magnetic head, the magnetic disk including tracks on which servo sectors storing servo information are disposed at intervals in a circumferential direction, the tracks including a first track and a second track, the second track being radially adjacent to the first track and being subject to writing earlier than the first track, each of the first track and the second track including data sectors, the data sectors including a data sector in which an error correction code for error correction in units of tracks is stored, the method comprising:

• reading servo information when the magnetic head passes over each of the servo sectors, acquiring a positional error signal of the magnetic head based on the read servo information, and executing a write operation on the first track while executing positioning of the magnetic head on the first track based on the positional error signal;
• executing a first operation during the write operation in response to the magnetic head passing over a first servo sector, which is one of the servo sectors, the first operation being executed by calculating, based on the positional error signal, an evaluation amount of damage to data of the second track caused by the write operation and comparing a first amount, which is the evaluation amount calculated based on the positional error signal, with a first threshold value corresponding to a correction limit of error correction in units of the tracks;
• executing a second operation by interrupting the write operation in response to determining that the first amount is larger than the first threshold value in the first operation, the second operation being executed by executing a read operation on the second track, acquiring a metric representing signal quality of data of the second track read by the read operation, calculating an evaluation amount based on the metric, and comparing a second amount, which is the evaluation amount calculated based on the metric with the first threshold value;
• continuing the write operation on the first track in response to determining that the first amount is smaller than the first threshold value in the first operation or determining that the second amount is smaller than the first threshold value in the second operation;
• and
• executing a protection operation of protecting data of the first track in response to determining that the second amount is larger than the first threshold value in the second operation.