Magnetic disk apparatus and method

A magnetic disk apparatus comprising:

• a magnetic disk on which multiple tracks are provided;
• a magnetic head;
• and
• a controller configured to
• move the magnetic head to a first track being one of the multiple tracks,
• acquire, in a servo sampling cycle, a positioning error amount of the magnetic head with respect to the first track,
• execute an access to the first track by using the magnetic head after a positioning error amount being equal to or less than a first threshold is continuously acquired a first set number of times,
• obtain a frequency estimation value by estimating a frequency of residual vibration of the magnetic head due to movement of the magnetic head to the first track and obtain an amplitude estimation value by estimating an amplitude of the residual vibration, and
• update the first set number of times on the basis of the frequency estimation value of the residual vibration and the amplitude estimation value of the residual vibration.