Magnetic disk device and method of managing parity

A method of managing parity applied to a magnetic disk device, the magnetic disk device comprising:

• a disk including a first track, the first track including a first data area in which first data is recorded and a first parity area in which first parity is recorded to reconstruct the first data in the first data area;
• and a storage section which stores information indicating whether the first parity area is a valid parity area in which the first parity is recorded or an invalid parity area in which the first parity is not recorded,
• the method comprising:
• determining presence or absence of an unexecuted command;
• and
• searching the storage section for the first parity area after it is determined that there is no unexecuted command, generating the first parity based on the first data in the first data area if the first parity area is detected as the invalid parity area, and writing the first parity to the first parity area.