Magnetic disk device

1. A magnetic disk device comprising:

a magnetic disk;

a magnetic head that is positioned on a track having a predetermined track pitch of the magnetic disk, writes data to the track of the magnetic disk, and reads data from the track of the magnetic disk; and

a controller that controls positioning of the magnetic head, and registers an address of a sector of the track in which the data is written and a positioning error of the magnetic head with respect to the track at the address, determines whether or not a positioning error of a second sector that is two tracks ahead in a radial direction of a first sector to which the data is written is registered, and when the positioning error of the second sector is registered, sets a first threshold that allows a write operation for a positioning error of the first sector based on the positioning error of the second sector, and determines whether or not the positioning error of the first sector exceeds the first threshold, and stops the write operation when the positioning error of the first sector exceeds the first threshold.

2. The magnetic disk device according to claim 1 , wherein

the controller registers both a positioning error in an inner radial direction and a positioning error in an outer radial direction.

3. The magnetic disk device according to claim 1 , wherein

the controller

sets a second threshold configured to determine registration of the positioning error of the first sector, and

determines whether or not the positioning error of the first sector exceeds the second threshold, and registers the positioning error of the first sector when the positioning error of the first sector exceeds the second threshold.

4. The magnetic disk device according to claim 2 , wherein

the controller

sets a second threshold configured to determine registration of the positioning error of the first sector,

determines whether or not the positioning error of the first sector exceeds the second threshold,

determines presence or absence of a registered positioning error in the first sector,

determines whether or not directions of the positioning error of the first sector and the registered positioning error match in either the radial inner direction or the outer radial direction,

determines whether or not an absolute value of the positioning error of the first sector is larger than the registered positioning error, and

registers the positioning error of the first sector when the positioning error of the first sector exceeds the second threshold, and the registered positioning error in the first sector exists, and the directions of the positioning error of the first sector and the registered positioning error match, and the absolute value of the positioning error of the first sector is larger than the registered positioning error.

5. The magnetic disk device according to claim 1 , wherein

the controller

determines whether or not a positioning error of a third sector adjacent to the first sector in the radial direction is registered,

determines whether or not a direction of the positioning error of the third sector is a direction toward the first sector, and

releases registration of the positioning error of the third sector when the positioning error of the third sector is registered and the direction of the positioning error of the third sector is the direction toward the first sector.

6. The magnetic disk device according to claim 1 , wherein

the first threshold is a value obtained by subtracting the positioning error of the second sector from a predetermined track pitch narrowing margin.

7. The magnetic disk device according to claim 5 , wherein

the first threshold is a value obtained by subtracting the positioning error of the second sector from a predetermined track pitch narrowing margin, and

the predetermined track pitch narrowing margin is a sum of the positioning error of the first sector and the positioning error of the second sector in which a track width of the third sector sandwiched between the first sector and the second sector becomes a lower limit for reading by writing the first sector and the second sector.

8. The magnetic disk device according to claim 6 , wherein

the controller

sets a third threshold that allows the write operation for the positioning error of the first sector when the positioning error of the second sector is not registered,

determines whether or not the positioning error of the first sector exceeds the third threshold, and

stops the write operation when the positioning error of the first sector exceeds the third threshold.

9. The magnetic disk device according to claim 8 , wherein

a range of the third threshold is from a half of the track pitch narrowing margin to the track pitch narrowing margin.

10. The magnetic disk device according to claim 3 , wherein

the first threshold is a value obtained by adding a predetermined amount to a predetermined track pitch narrowing margin and subtracting a product of a predetermined gain and the positioning error of the second sector.

11. The magnetic disk device according to claim 10 , wherein

the predetermined amount is a product of a value obtained by subtracting 1 from the predetermined gain and the second threshold.

12. The magnetic disk device according to claim 1 , wherein

the first threshold is a value obtained by subtracting a product of a predetermined gain and the positioning error of the second sector from a predetermined track pitch narrowing margin.

13. The magnetic disk device according to claim 10 , wherein

the predetermined gain has a value of 1 or more.

14. The magnetic disk device according to claim 12 , wherein

the predetermined gain has a value of 1 or more.