Disk drive with distributed codeword blocks

• US 9,059,737 B2
• Filed: 05/01/2013
• Issued: 06/16/2015
• Est. Priority Date: 01/11/2013
• Status: Active Grant

• Current Assignee: JP Morgan Chase Bank, N.A. (JP Morgan Chase & Co)
• Original Assignee: HGST Netherlands B.V. (Western Digital Corporation)
• Inventors: Coker, Jonathan Darrel, Galbraith, Richard Leo, Hanson, Weldon Mark, Oenning, Travis Roger, Wood, Roger William
• Primary Examiner(s): MCMAHON, DANIEL F
• Application Number:
  US13/875,165
• Publication Number:
  US 20140201590A1
• Time in Patent Office: 776 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G11B 20/1217 on discs
• 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: H03M 13/09 Error detection only, e.g. using cyclic redundancy check [CRC] codes or single parity bit
• 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 13/27 using interleaving techniques
• CPC Class Codes: H03M 13/373 with erasure correction and erasure determination, e.g. for packet loss recovery or setting of erasures for the decoding of Reed-Solomon codes
• CPC Class Codes: H03M 13/3761 using code combining, i.e. using combining of codeword portions which may have been transmitted separately, e.g. Digital Fountain codes, Raptor codes or Luby Transform [LT] codes

Abstract

Disk drives are described in which blocks of data spanning multiple sectors are encoded into a plurality of codewords which are then divided into segments that are physically separated (distributed) on the disk surface over multiple sectors in a distributed codeword block so that the codewords have an improved worst case SNR in comparison to individual sectors. This results in more even SNR performance for each codeword, which improves the performance for portions of a track which have lower than the average SNR. Embodiments are described in which the distributed codeword blocks span across tracks.

Claims

1. A method for storing and retrieving blocks of data in a disk drive that has data stored in tracks on a disk that include a plurality of sectors, the method comprising:

generating a plurality of codewords from a logical block of data, the logical block of data having a predetermined size corresponding to a selected number of sectors, each codeword containing a selected portion of the data from the logical block of data along with additional bits used for error detection;

dividing each of the plurality of codewords into a plurality of segments;

forming a distributed codeword block that corresponds to the selected number of sectors by arranging the plurality of segments of each codeword in a predetermined pattern wherein segments of each codeword are positioned in more than one sector; and

writing the distributed codeword block into the selected number of sectors on the disk, wherein a plurality of distributed codeword blocks stored on the disk and the codewords in the distributed codeword blocks have a minimum SNR that is equal to or higher than a minimum SNR for individual sectors.

2. The method of claim 1 wherein generating the plurality of codewords further comprises dividing the logical block of data in a set of equal sized units that processed by an encoder that generates a set of parity bits that are included in each codeword.

3. The method of claim 2 wherein the encoder uses a low-density parity-check (LDPC) code.

4. The method of claim 3 wherein the encoder distributes the parity bits in a predetermined plurality of positions inside each codeword.

5. The method of claim 1 wherein the additional bits used for error detection in each codeword include CRC bits.

6. The method of claim 5 wherein dividing each of the plurality of codewords into a plurality of segments, further comprises placing all of the CRC bits in a selected codeword in one segment.

7. The method of claim 1 wherein writing the distributed codeword block into the selected number of sectors on the disk, further comprises writing the selected number of sectors on at least first and second tracks wherein the distributed codeword block is distributed across at least two tracks.

9. The method of claim 1 further comprising retrieving the logical block of data by reading the distributed codeword block, reassembling the plurality of codewords from the plurality of segments, processing the codewords through a decoder to detect errors and retrieve the selected portion of the data in each codeword, and combining the selected portions of the data to obtain the logical block of data.

8. A method for storing and retrieving logical blocks of data in a disk drive that has data stored in tracks on a disk that include a plurality of sectors, the method comprising:

generating a plurality of codewords from a logical block of data, the logical block of data having a predetermined size corresponding to a selected number of sectors, each codeword containing a selected portion of the data from the logical block of data along with additional bits used for error detection;

dividing each of the plurality of codewords into a plurality of segments;

forming a distributed codeword block that corresponds to the selected number of sectors by arranging the plurality of segments of each codeword in a predetermined pattern wherein segments of each codeword are positioned in more than one sector; and

writing the distributed codeword block into the selected number of sectors on the disk, wherein a plurality of distributed codeword blocks stored on the disk and the codewords in the distributed codeword blocks have a minimum SNR that is equal to or higher than a minimum SNR for individual sectors; and

wherein writing the distributed codeword block into the selected number of sectors on the disk, further comprises writing the sectors on at least first and second tracks wherein the distributed codeword block is distributed across at least two tracks; and

wherein the first and second tracks are adjacent on the disk with anti-correlated squeeze and adverse effects of track squeeze are reduced by distributing the codewords across at least two tracks.

10. A method for storing and retrieving logical blocks of data in a disk drive that has data stored in tracks on a disk that include a plurality of sectors, the method comprising:

generating a plurality of codewords from at least first and second logical blocks of data including sectors designated for first and second tracks, the logical blocks of data having a predetermined size corresponding to a selected number of sectors on each track, each codeword containing a selected portion of the data from the logical block of data along with additional bits used for error detection;

dividing each of the plurality of codewords into a plurality of segments;

forming a distributed codeword block that includes the selected number of sectors on each track by arranging the plurality of segments of each codeword in a predetermined pattern wherein segments of each codeword are distributed in more than one sector and on more than one track; and

writing the distributed codeword block into the selected number of sectors on at least first and second tracks on the disk, wherein the codewords in the distributed codeword blocks have a minimum SNR that is equal to or higher than a minimum SNR for individual sectors.

11. The method of claim 10 wherein generating the plurality of codewords further comprises dividing the logical block of data in a set of equal sized units that processed by an encoder that generates a set of parity bits that are included in each codeword.

12. The method of claim 11 wherein the encoder uses a low-density parity-check (LDPC) code.

13. The method of claim 12 wherein the encoder distributes parity bits in a predetermined plurality of positions inside each codeword.

14. The method of claim 10 wherein the additional bits used for error detection in each codeword include CRC bits.

15. The method of claim 14 wherein dividing each of the plurality of codewords into a plurality of segments, further comprises placing all of the CRC bits in a selected codeword in one of the segments of the selected codeword.

16. A method for storing and retrieving logical blocks of data in a disk drive that has data stored in tracks on a disk that include a plurality of sectors, the method comprising:

generating a plurality of codewords from at least first and second logical blocks of data including sectors designated for first and second tracks, the logical blocks of data having a predetermined size corresponding to a selected number of sectors on each track, each codeword containing a selected portion of the data from the logical block of data along with additional bits used for error detection;

dividing each of the plurality of codewords into a plurality of segments;

forming a distributed codeword block that includes the selected number of sectors on each track by arranging the plurality of segments of each codeword in a predetermined pattern wherein segments of each codeword are distributed in more than one sector and on more than one track; and

writing the distributed codeword block into the selected number of sectors on at least first and second tracks on the disk, wherein the codewords in the distributed codeword blocks have a minimum SNR that is equal to or higher than a minimum SNR for individual sectors; and

wherein the first and second tracks are adjacent on the disk with anti-correlated squeeze and adverse effects of track squeeze are reduced by distributing the codewords across at least two tracks.

17. A disk drive comprising:

a codeword encoder;

a codeword block distribution unit that processes a logical block of data corresponding to a selected number of sectors into a plurality of codewords using the codeword encoder, divides each codeword into a plurality of segments and distributes the plurality of segments of each codeword in a predetermined pattern in a distributed codeword block that spans the selected number of sectors so that the segments of each codeword are distributed between a plurality of sectors; and

a read/write channel that writes the distributed codeword block on one or more tracks on the disk, wherein the codewords in the distributed codeword blocks have a minimum SNR that is equal to or higher than a minimum SNR for individual sectors.