Iterating inner and outer codes for data recovery

• US 9,015,549 B2
• Filed: 04/26/2011
• Issued: 04/21/2015
• Est. Priority Date: 04/26/2011
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Rub, Bernardo, Patapoutian, Ara, Sridharan, Arvind, Buch, Bruce D.
• Primary Examiner(s): NGUYEN, STEVE N
• Application Number:
  US13/094,048
• Publication Number:
  US 20120278679A1
• Time in Patent Office: 1,456 Days
• Field of Search: None
• US Class Current: 714/755
• CPC Class Codes: G11B 20/1833 by adding special lists or symbols to the coded information G11B20/1806, G11B20/1866 take precedence
• CPC Class Codes: G11B 2020/1836 using a Reed Solomon [RS] code
• CPC Class Codes: G11B 2020/1853 using a product code which has inner and outer parity symbols
• CPC Class Codes: G11B 2220/2516 Hard disks
• CPC Class Codes: H03M 13/1102 Codes on graphs and decoding on graphs, e.g. low-density parity check [LDPC] codes
• CPC Class Codes: H03M 13/1515 Reed-Solomon codes
• CPC Class Codes: H03M 13/2909 Product codes
• CPC Class Codes: H03M 13/2927 Decoding strategies
• CPC Class Codes: H03M 13/3746 with iterative decoding

Abstract

A storage medium includes at least one data unit defining a plurality of symbol-based inner code words and a plurality of symbol-based outer code words. Each symbol included in one of the inner code words is also included in one of the outer code words. A processor is configured to perform a first iteration of inner code error correction on the plurality of symbol-based inner code words, a first iteration of outer code error correction on the plurality of symbol-based outer code words and a second iteration of inner code error correction on the plurality of symbol-based inner code words. In the first iteration of outer code error corrections, at least one of the outer code words is correctable. In the second iteration of inner code error correction, at least one of the inner code words is correctable.

Claims

1. A method comprising:

performing a first iteration of an inner code word error correction process including;

determining if an inner code can correct errors in a first selected inner code word of multiple inner code words;

when the inner code can correct the first selected inner code word, performing an inner code error correction on the first selected inner code word;

repeating the inner code word error correction process for another selected inner code word of the multiple inner code words;

performing a first iteration of an outer code word error correction process when there are uncorrected inner code words, including;

determining if an outer code can correct errors in a first selected outer code word of multiple outer code words wherein each symbol included in one of the inner code words is also included in one of the outer code words;

when the outer code can correct the first selected outer code word, performing an outer code error correction on the first selected outer code;

repeating the outer code word error correction process for another selected outer code word of the multiple outer code words; and

performing a second iteration of the inner code word error correction process when there are uncorrected outer code words.

2. The method of claim 1, wherein performing the first iteration of inner code error correction process comprises:

selecting inner code words to determine selected inner code words; and

determining whether errors in the selected inner code words can be corrected by the inner code.

3. The method of claim 2, wherein if the errors in at least one of the selected inner code words fails to be corrected by the inner code, then perform the first iteration of the outer code word error correction process.

4. The method of claim 1, wherein performing the first iteration of the outer code word error correction process comprises:

selecting outer code words to determine selected outer code words; and

determining whether errors in the selected outer code words can be corrected by the outer code.

6. The method of claim 1, wherein performing the second iteration of the inner code word error correction process comprises:

selecting inner code words to determine selected inner code words; and

determining whether errors in the selected inner code words can be corrected by the inner code.

7. The method of claim 6, wherein if the errors in at least one of the selected inner code words fails to be corrected by the inner code, then perform a second iteration of the outer code word error correction process.

8. The method of claim 1, further comprising performing a second iteration of the outer code word error correction process if errors in at least one inner code word fails to be corrected by the inner code word correction process after the second iteration of the inner code word error correction process.

9. The method of claim 1, further comprising when the inner code cannot correct errors in the first selected inner code word, then initiating the outer code word error correction process without performing an inner code error correction on the first selected inner code word.

10. The method of claim 1, further comprising when the outer code cannot correct errors in the first selected outer code word, then initiating the inner code word error correction process without performing an outer code error correction on the first selected outer code.

5. The method of 4, wherein if the errors in at least one of the selected outer code words fails to be corrected by the outer code, then perform the second iteration of the inner code word error correction process.

11. An apparatus comprising:

a data storage medium including at least one data unit defining a plurality of symbol-based inner code words and a plurality of symbol-based outer code words, wherein each symbol included in one of the inner code words is also included in one of the outer code words;

a processor configured to perform a data recovery process including;

determine if an inner code can correct errors in a selected inner code word of the plurality of symbol-based inner code words;

when the inner code can correct the selected inner code word, perform inner code error correction on the selected inner code word;

when the inner code cannot correct all errors in the plurality of symbol-based inner code words, determine if an outer code can correct errors in a selected outer code word of the plurality of symbol-based outer code words;

when the outer code can correct the selected outer code word, perform outer code error correction on the selected outer code word; and

when the outer code cannot correct all errors in the plurality of symbol-based outer code words, repeat the data recovery process.

12. The apparatus of claim 11, wherein each data unit in the storage medium further comprises a plurality of segments for storing data, the plurality of segments including k number of segments and r number of segments, each of the k and r number of segments being one of the inner code words and including inner code parity for providing inner code protection against errors within the inner code word, each of the r number of segments including outer code parity for providing outer code protection against inner code failures.

13. The apparatus of claim 11, further comprising the processor is configured to:

select inner code words to produce selected inner code words;

determine whether errors in the selected inner code words can be corrected by the inner code; and

when errors in at least one of the selected inner code words fails to be corrected by the inner code, then the processor performs the outer code error correction.

14. The apparatus of claim 11, further comprising the processor is configured to:

select outer code words to produce selected outer code words;

determine whether errors in the selected outer code words can be corrected by the outer code; and

when errors in at least one of the selected outer code words fails to be corrected by the outer code, then the processor performs the inner code error correction.

15. The apparatus of claim 11, wherein the data storage medium comprises a shingled magnetic recording medium.

16. The apparatus of claim 11, further comprising the data recovery process including:

when the inner code cannot correct errors in the selected inner code word, then proceeding to determining if an outer code can correct errors in the selected outer code word of the plurality of outer code words without performing inner code error correction on the selected inner code word.

17. The apparatus of claim 11, further comprising the data recovery process including:

when the outer code cannot correct errors in the selected outer code word, then proceeding to determining if the inner code can correct errors in the selected inner code word of the plurality of inner code words without performing outer code error correction on the selected outer code word.

18. A method comprising:

performing a data recovery process on data from a data storage medium including at least one data unit having a plurality of segments for storing data, the plurality of segments including k number of segments and r number of segments, each k and r segment including an inner code parity for providing inner code protection against errors within the segment and each r segment including outer code parity for providing outer code protection against inner code failures;

associating the r number of segments with the k number of segments to derive a plurality of outer code words, wherein each outer code word contains m number of symbols from each segment for correcting m number of symbols in each outer code word;

iteratively performing an error correction process by;

determining if an inner code can correct errors in a first selected inner code word of the plurality of inner code words;

when the inner code can correct errors in the first selected inner code word, then performing inner code error correction on the plurality of inner code words;

when an error in at least one of the plurality of inner code words fails to be corrected by the inner code, then determining if an outer code can correct errors in a first selected outer code word of the plurality of outer code words;

when the outer code can correct errors in the first selected outer code word, then performing outer code error correction on the plurality of outer code words; and

when an error in at least one of the plurality of outer code words fails to be corrected by the outer code, then repeating the error correction process;

wherein k, r and m are integers greater than or equal to 1.

19. The method of claim 18, further comprising the error correction process including when the inner code cannot correct errors in the first selected inner code word, then proceeding to determining if an outer code can correct errors in a first selected outer code word of the plurality of outer code words without performing inner code error correction on the plurality of inner code words.

20. The method of claim 19, further comprising the error correction process including when the outer code cannot correct errors in the first selected outer code word, then proceeding to determining if an inner code can correct errors in a first selected inner code word of the plurality of inner code words without performing outer code error correction on the plurality of outer code words.