Magnetic disk device and data protection method thereof

A data protection method in a magnetic disk device, the data protection method comprising:

• monitoring a supply voltage supplied to a plurality of actuators each executing processing of reading/writing data from/to a magnetic disk by using a first threshold value at which power supply by back electromotive force of a motor for rotating the magnetic disk is started, and a second threshold value that is higher than the first threshold value;
• in a case where the supply voltage is lower than or equal to the second threshold value and is higher than the first threshold value, interrupting execution of the processing in at least one of the actuators according to a predetermined condition based on execution status of the processing in the actuators;
• after the processing is interrupted, in a case where the supply voltage has decreased to a value lower than or equal to the first threshold value, starting power supply by back electromotive force of the motor, and saving the data that has not been read from or written to the magnetic disk at the time of starting of the power supply;
• and
• after the processing is interrupted, in a case where the supply voltage has increased to a value higher than the second threshold value, restarting the interrupted processing.