Storage device, data-assurance control device, and data assurance method

1. A storage device that performs an assurance of read-data that is read by an offset-reading retry process of retrying an offset reading in an inner direction toward a center of a storage medium and in an outer direction toward a circumference of the storage medium, when a data read-error occurs near a track center of the storage medium, the storage device comprising:

a data reading unit that reads inner offset data from an inner-direction offset reading and outer offset data from an outer-direction offset reading;

a data comparing unit that compares the inner offset data and the outer offset data read by the data reading unit; and

a data-output control unit that outputs the read-data when a result of comparison by the data comparing unit indicates that the inner offset data matches the outer offset data.

2. The storage device according to claim 1 , wherein

when reading of either one of the inner offset data and the outer offset data by the data reading unit is successful, the data-output control unit outputs the read-data that is successfully read.

3. The storage device according to claim 1 , wherein

when the inner offset data does not match the outer offset data, the data reading unit performs the offset-reading by decreasing offset amounts in the inner direction and the outer direction by the same amount in a stepwise manner, and

when an error occurs in one of the inner-direction offset reading and the outer-direction offset reading and when other of the inner-direction offset reading and the outer-direction offset reading is performed normally, the data-output control unit outputs the read-data obtained by the other of the inner-direction offset reading and the outer-direction offset reading.

4. The storage device according to claim 3 , further comprising:

a read-data overwriting unit that overwrites, when the read-data obtained by the other of the inner-direction offset reading and the outer-direction offset reading is output, the read-data in an entire region of a track and a sector from which reading of the read-data is successful.

5. The storage device according to claim 4 , further comprising:

a selecting unit that selects, when the read-data obtained by the other of the inner-direction offset reading and the outer-direction offset reading is output, whether to overwrite the read-data in the entire region of the track and the sector from which reading of the read-data is successful.

6. The storage device according to claim 1 , wherein

when either one of the inner-direction offset reading and the outer-direction offset reading is successful, the data reading unit performs the offset-reading by increasing offset amounts in the inner direction and the outer direction by the same amount in a stepwise manner, and

when an error occurs in one of the inner-direction offset reading and the outer-direction offset reading and when other of the inner-direction offset reading and the outer-direction offset reading is performed normally, the data-output control unit outputs the read-data obtained by the other of the inner-direction offset reading and the outer-direction offset reading.

7. The storage device according to claim 6 , further comprising:

a read-data overwriting unit that overwrites, when the read-data obtained by the other of the inner-direction offset reading and the outer-direction offset reading is output, the read-data in an entire region of a track and a sector from which reading of the read-data is successful.

8. The storage device according to claim 7 , further comprising:

a selecting unit that selects, when the read-data obtained by the other of the inner-direction offset reading and the outer-direction offset reading is output, whether to overwrite the read-data in the entire region of the track and the sector from which reading of the read-data is successful.

9. The storage device according to claim 1 , wherein

when the inner offset data does not match the outer offset data, the data-output control unit outputs read-error information.

10. The storage device according to claim 9 , further comprising:

an uncorrectable-data overwriting unit that overwrites, when the read-error information is output by the data-output control unit, uncorrectable data that is uncorrectable by an error correcting code in an entire region of a track and a sector from which the read-error occurred.

11. The storage device according to claim 10 , further comprising:

a selecting unit that selects whether to overwrite the uncorrectable data in the entire region of the track and the sector from which the read-error occurred.

12. The storage device according to claim 1 , wherein

when either one of the inner-direction offset reading and the outer-direction offset reading is successful, the data reading unit performs the offset-reading by increasing offset amounts in the inner direction and the outer direction by the same amount in a stepwise manner, and

when both the inner-direction offset reading and the outer-direction offset reading by the data reading unit are successful and when the inner offset data does not match the outer offset data, the data-output control unit outputs read-error information.

13. The storage device according to claim 12 , further comprising:

an uncorrectable-data overwriting unit that overwrites, when the read-error information is output by the data-output control unit, uncorrectable data that is uncorrectable by an error correcting code in an entire region of a track and a sector from which the read-error occurred.

14. The storage device according to claim 13 , further comprising:

a selecting unit that selects whether to overwrite the uncorrectable data in the entire region of the track and the sector from which the read-error occurred.

15. The storage device according to claim 1 , further comprising:

a selecting unit that, when the inner offset data does not match the outer offset data, selects one from

outputting read-error information; and

outputting the read-data obtained by performing the offset-reading by decreasing offset amounts in the inner direction and the outer direction by the same amount in a stepwise manner, the read-data being obtained by the offset data that is performed normally when an error occurs in one of the inner-direction offset reading and the outer-direction offset reading and when other of the inner-direction offset reading and the outer-direction offset reading is performed normally.

16. The storage device according to claim 1 , further comprising:

a selecting unit that, when a data reading of either one of the inner offset data and the outer offset data by the data reading unit is successful, selects one from outputting the read-data that is successfully read; and

outputting the read-data obtained by performing the offset-reading by decreasing offset amounts in the inner direction and the outer direction by the same amount in a stepwise manner, the read-data being obtained by the offset data that is performed normally when an error occurs in one of the inner-direction offset reading and the outer-direction offset reading and when other of the inner-direction offset reading and the outer-direction offset reading is performed normally.

17. A data-assurance control apparatus that performs an assurance of read-data that is read by an offset-reading retry process of retrying an offset reading in an inner direction toward a center of a storage medium and in an outer direction toward a circumference of the storage medium, when a data read-error occurs near a track center of the storage medium, the data-assurance control apparatus comprising:

a data comparing unit that compares inner offset data read from an inner-direction offset reading and outer offset data read from an outer-direction offset reading; and

a data-output control unit that outputs the read-data when a result of comparison by the data comparing unit indicates that the inner offset data matches the outer offset data.

18. The data-assurance control apparatus according to claim 17 , wherein

when reading of either one of the inner offset data and the outer offset data is successful, the data-output control unit outputs the read-data that is successfully read.

19. The data-assurance control apparatus according to claim 17 , wherein

when the inner offset data does not match the outer offset data, the offset-reading is performed by decreasing offset amounts in the inner direction and the outer direction by the same amount in a stepwise manner, and

when an error occurs in one of the inner-direction offset reading and the outer-direction offset reading and when other of the inner-direction offset reading and the outer-direction offset reading is performed normally, the data-output control unit outputs the read-data obtained by the other of the inner-direction offset reading and the outer-direction offset reading.

20. A read-data assurance method of performing an assurance of read-data that is read by an offset-reading retry process of retrying an offset reading in an inner direction toward a center of a storage medium and in an outer direction toward a circumference of the storage medium, when a data read-error occurs near a track center of the storage medium, the read-data assurance method comprising:

reading inner offset data from an inner-direction offset reading and outer offset data from an outer-direction offset reading;

comparing the inner offset data and the outer offset data read at the reading; and

outputting the read-data when a result of comparison at the comparing indicates that the inner offset data matches the outer offset data.