Magnetic disk apparatus and method

1. A magnetic disk apparatus comprising:

a magnetic disk provided with a track including a plurality of first sectors, the plurality of first sectors including a plurality of second sectors where data segments are written and a third sector where parity and first information indicating effectiveness or ineffectiveness of protection by the parity are written;

a magnetic head; and

a controller configured to access the magnetic disk by using the magnetic head, wherein

the controller is configured to, when implementing write to all the plurality of second sectors,

generate parity on the basis of all data segments written to the plurality of second sectors, and

write, to the third sector, the parity and a value indicating effectiveness of the protection by the parity as the first information, and

the controller is configured to, when implementing overwrite to part of the plurality of second sectors after the write to all the plurality of second sectors,

overwrite a value indicating ineffectiveness of the protection by the parity as the first information.

2. A magnetic disk apparatus comprising:

a magnetic disk provided with a track including a plurality of first sectors, the plurality of first sectors including a plurality of second sectors where data segments are written and a third sector where parity and first information indicating effectiveness or ineffectiveness of protection by the parity are written;

a magnetic head; and

a controller configured to access the magnetic disk by using the magnetic head, wherein

the controller is configured to, when implementing write to all the plurality of second sectors,

write, to each second sector in the plurality of second sectors, a data segment and a value indicating effectiveness of the protection by the parity as second information,

generate parity on the basis of all data segments written to the plurality of second sectors, and

write, to the third sector, the parity and the value indicating effectiveness of the protection by the parity as the first information, and

the controller is configured to, when implementing overwrite to one or more fourth sectors being part of the plurality of second sectors after the write to all the plurality of second sectors,

overwrite, to the one or more fourth sectors, a data segment and a value indicating ineffectiveness of the protection by the parity as the second information, and

overwrite, to the third sector, the value indicating ineffectiveness of the protection by the parity as the first information.

3. The magnetic disk apparatus according to claim 2 , wherein the controller is configured to

implement read from the plurality of first sectors,

start error correction using all data segments read from the plurality of second sectors and the parity read from the third sector,

use the data segments obtained by the error correction when all the second information read from the plurality of second sectors and the first information read from the third sector indicate effectiveness of the protection by the parity, and

abort the error correction or discard the data segments obtained by the error correction when either the second information read from the plurality of second sectors or the first information read from the third sector indicates ineffectiveness of the protection by the parity.

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

the controller is configured to

read one or more fifth sectors being one or more second sectors in the plurality of second sectors, and

implement read from the plurality of first sectors including re-implementation of read from the one or more fifth sectors when the read from the one or more fifth sectors fails, and

the controller is configured to, after the re-implementation of read from the one or more fifth sectors fails,

implement error correction using the parity when all the second information and the first information read from the plurality of first sectors indicate the effectiveness of the protection by the parity, and

perform no error correction using the parity when either all the second information or the first information read from the plurality of first sectors indicates the ineffectiveness of the protection by the parity.

5. A magnetic disk apparatus comprising:

a magnetic disk provided with a track including a plurality of first sectors, the plurality of first sectors including a plurality of second sectors where data segments are written and a third sector where parity and first information are written, the first information indicating a range where protection by the parity is effective in the plurality of second sectors;

a magnetic head; and

a controller configured to access the magnetic disk by using the magnetic head, wherein the controller is configured to, when implementing one or more fourth sectors being one or more second sectors in the plurality of second sectors,

generate parity on the basis of all data segments written to the one or more fourth sectors, and

write, to the third sector, the parity and a value as the first information indicating the one or more fourth sectors.

6. The magnetic disk apparatus according to claim 5 , wherein

the controller is configured to

implement read from one or more fifth sectors being one or more second sectors in the plurality of second sectors,

implement read from the plurality of first sectors after the read from the one or more fifth sectors fails and start first error correction using all data segments read from the plurality of second sectors and the parity read from the third sector,

use the data segments obtained by the first error correction when the one or more fourth sectors indicated by the first information match the plurality of second sectors, and

abort the first error correction or discard the data segments obtained by the first error correction when the one or more fourth sectors indicated by the first information do not match the plurality of second sectors, and

the controller is configured to, after the first error correction is aborted or the data segments obtained by the first error correction are discarded,

implement read from the one or more fourth sectors and the third sector when the one or more fifth sectors are included in the one or more fourth sectors indicated by the first information,

start second correction using all data segments read from the one or more fourth sectors and the parity read from the third sector, and

use the data segments obtained by the second error correction.

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

the controller is configured to

implement read from one or more fifth sectors being one or more second sectors in the plurality of second sectors, and

re-implement read from the one or more fifth sectors when the read of the one or more fifth sectors fails and implement read of the first information when the magnetic head passes through the third sector in the re-implementation of the read from the one or more fifth sectors, and

the controller is configured to, after the re-implementation of read from the one or more fifth sectors fails,

implement error correction using the parity when the one or more fifth sectors are included in the one or more fourth sectors indicated by the first information, and

perform no error correction using the parity when the one or more fifth sectors are not included in the one or more fourth sectors indicated by the first information.

8. A method of controlling a magnetic disk apparatus including a magnetic disk provided with a track including a plurality of first sectors, the plurality of first sectors including a plurality of second sectors where data segments are written and a third sector where parity and first information indicating effectiveness or ineffectiveness of protection by the parity are written, the method comprising:

when implementing write to all the plurality of second sectors,

generating parity on the basis of all data segments written to the plurality of second sectors, and

writing, to the third sector, the parity and a value indicating effectiveness of the protection by the parity as the first information; and

when implementing overwrite to part of the plurality of second sectors after the write to all the plurality of second sectors,

overwriting a value indicating ineffectiveness of the protection by the parity as the first information.

9. The method according to claim 8 , further comprising:

when implementing write to all the plurality of second sectors,

writing, to each second sector in the plurality of second sectors, a data segment and a value indicating effectiveness of the protection by the parity as second information,

generating parity on the basis of all data segments written to the plurality of second sectors, and

writing, to the third sector, the parity and the value indicating effectiveness of the protection by the parity as the first information; and,

when implementing overwrite to one or more fourth sectors being part of the plurality of second sectors after the write to all the plurality of second sectors,

overwriting, to the one or more fourth sectors, a data segment and a value indicating ineffectiveness of the protection by the parity as the second information, and

overwriting, to the third sector, the value indicating ineffectiveness of the protection by the parity as the first information.

10. The method according to claim 9 , further comprising:

implementing read from the plurality of first sectors;

starting error correction using all data segments read from the plurality of second sectors and the parity read from the third sector;

using the data segments obtained by the error correction when all the second information read from the plurality of second sectors and the first information read from the third sector indicate effectiveness of the protection by the parity; and

aborting the error correction or discarding the data segments obtained by the error correction when either the second information read from the plurality of second sectors or the first information read from the third sector indicates ineffectiveness of the protection by the parity.

11. The method according to claim 9 , further comprising:

reading one or more fifth sectors being one or more second sectors in the plurality of second sectors;

implementing read from the plurality of first sectors including re-implementation of read from the one or more fifth sectors when the read from the one or more fifth sectors fails; and

after the re-implementation of read from the one or more fifth sectors fails,

implementing error correction using the parity when all the second information and the first information read from the plurality of first sectors indicate the effectiveness of the protection by the parity, and

performing no error correction using the parity when either all the second information or the first information read from the plurality of first sectors indicates the ineffectiveness of the protection by the parity.

12. A method of controlling a magnetic disk apparatus including a magnetic disk provided with a track including a plurality of first sectors, the plurality of first sectors including a plurality of second sectors where data segments are written and a third sector where parity and first information are written, the first information indicating a range where protection by the parity is effective in the plurality of second sectors, the method comprising:

when implementing one or more fourth sectors being one or more second sectors in the plurality of second sectors,

generating parity on the basis of all data segments written to the one or more fourth sectors; and

writing, to the third sector, the parity and a value as the first information indicating the one or more fourth sectors.

13. The method according to claim 12 , further comprising:

implementing read from one or more fifth sectors being one or more second sectors in the plurality of second sectors;

implementing read from the plurality of first sectors after the read from the one or more fifth sectors fails and start first error correction using all data segments read from the plurality of second sectors and the parity read from the third sector;

using the data segments obtained by the first error correction when the one or more fourth sectors indicated by the first information match the plurality of second sectors;

aborting the first error correction or discarding the data segments obtained by the first error correction when the one or more fourth sectors indicated by the first information do not match the plurality of second sectors; and,

after the first error correction is aborted or the data segments obtained by the first error correction are discarded,

implementing read from the one or more fourth sectors and the third sector when the one or more fifth sectors are included in the one or more fourth sectors indicated by the first information,

starting second correction using all data segments read from the one or more fourth sectors and the parity read from the third sector, and

using the data segments obtained by the second error correction.

14. The method according to claim 12 , further comprising:

implementing read from one or more fifth sectors being one or more second sectors in the plurality of second sectors;

re-implementing read from the one or more fifth sectors when the read of the one or more fifth sectors fails and implement read of the first information when the magnetic head passes through the third sector in the re-implementation of the read from the one or more fifth sectors; and,

after the re-implementation of read from the one or more fifth sectors fails,

implementing error correction using the parity when the one or more fifth sectors are included in the one or more fourth sectors indicated by the first information, and

performing no error correction using the parity when the one or more fifth sectors are not included in the one or more fourth sectors indicated by the first information.