Magnetic disk device and method

A method of controlling a magnetic disk device including a magnetic disk, a magnetic head that writes and reads data to and from the magnetic disk, and a memory, the method comprising:

• storing a first data segment with first information piece in each of a plurality of first sectors, the first information piece being attribute information of a first sector storing thereof out of the plurality of first sectors, the magnetic disk being provided with a first track, the firs track including the plurality of first sectors and a second sector;
• storing a first parity in the second sector;
• and
• in a case where write of a second data segment to a third sector that is one of the plurality of first sectors is requested from a host,
• acquiring the second data segment from the host and storing the second data segment in the memory,
• reading a first data set that includes all first data segments and all first information pieces from the first track and stores the first data set in the memory,
• acquiring a second information piece that is attribute information of the third sector,
• updating, in the memory, a third data segment and a third information piece that are a first data segment and a first information piece read from the third sector out of the first data set with the second data segment and the second information piece,
• calculating a second parity on a basis of a second data set that is the first data set after update while writing the second data set to the first track, and
• writing the second parity in the second sector.