EFFICIENT REWRITE USING LARGER CODEWORD SIZES

• US 20190311741A1
• Filed: 06/24/2019
• Published: 10/10/2019
• Est. Priority Date: 12/19/2017
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Cideciyan, Roy D., Furrer, Simeon, Lantz, Mark A.
• Granted Patent: US 11,031,042 B2
• Time in Patent Office: Days
• CPC Class Codes: G11B 20/1201 on tapes
• 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 20/1886 with tapes
• CPC Class Codes: G11B 2020/184 using a cross-interleaved Reed Solomon [CIRC]
• CPC Class Codes: G11B 5/00813 magnetic tapes
• CPC Class Codes: H03M 13/1515 Reed-Solomon codes
• CPC Class Codes: H03M 13/27 using interleaving techniques
• CPC Class Codes: H03M 13/2792 Interleaver wherein interleaving is performed jointly with another technique such as puncturing, multiplexing or routing

Abstract

In one embodiment, a method includes writing a data set to a sequential access medium. The method also includes reading the data set after being written in a read-while-write process to identify faulty encoded data blocks, each of the faulty encoded data blocks including at least one faulty codeword. Moreover, the method includes rewriting a correct version of a first of the encoded data blocks in a first encoded data block set to the rewrite area of the sequential access medium selected from a predetermined subset of logical tracks. The predetermined subset of logical tracks includes D1+D2+1 logical tracks. Only one encoded data block from a particular sub data set is rewritten in a single encoded data block set in the rewrite area.

Claims

1. A system, comprising:

a magnetic head having a plurality of write transducers numbering at least M and a plurality of read transducers numbering at least M, each read transducer being configured to read data from a sequential access medium after being written thereto by a corresponding write transducer; and

a controller and logic integrated with and/or executable by the controller, the logic being configured to;

write, using the write transducers, a data set to a sequential access medium, the data set comprising a number of sub data sets of fixed size, each sub data set comprising a plurality of encoded data blocks comprising codewords, each codeword comprising a predetermined number of symbols;

read, using the read transducers, the data set in a read-while-write process to identify faulty encoded data blocks, each of the faulty encoded data blocks comprising at least one faulty codeword;

select a particular logical track from a predetermined subset of logical tracks in a rewrite area of the sequential access medium to rewrite the faulty encoded data blocks, the rewrite area being positioned subsequent to a position of the data set on the sequential access medium, wherein the predetermined subset of logical tracks includes D1+D2+1 logical tracks, and wherein 0<

D1+D2<

M/4; and

rewrite a correct version of a first of the encoded data blocks identified as faulty in a first encoded data block set to the rewrite area of the sequential access medium, wherein only one encoded data block from a particular sub data set is rewritten in a single encoded data block set in the rewrite area.

2. The system as recited in claim 1, wherein each of the symbols are 10 bits in size, and wherein the logic is further configured to:

select a second logical track from the predetermined subset of logical tracks in the rewrite area of the sequential access medium; and

rewrite a correct version of a second of the faulty encoded data blocks within the first encoded data block set to the second logical track in response to the first encoded data block being from a different sub data set than the second of the encoded data blocks.

3. The system as recited in claim 1, wherein each of the predetermined subsets of logical tracks comprises three logical tracks in sequence corresponding to D1=1 and D2=1.

4. The system as recited in claim 1, wherein each of the predetermined subsets of logical tracks comprises five logical tracks in sequence corresponding to D1=2 and D2=2.

5. The system as recited in claim 1, wherein each encoded data block is written to the sequential access medium as four symbol-interleaved Reed-Solomon RS(240,228) C1 codewords over a Galois Field GF(256).

6. The system as recited in claim 1, wherein each encoded data block is written to the sequential access medium as two symbol-interleaved Reed-Solomon RS(384,364) C1 codewords over a Galois Field GF(1024).

7. The system as recited in claim 1, wherein each encoded data block is written to the sequential access medium as one Reed-Solomon RS(768,728) C1 codeword over a Galois Field GF(1024).

8. The system as recited in claim 1, wherein the logic is further configured to decode the data set read from the sequential access medium to determine the faulty encoded data blocks, wherein an encoded data block is determined to be faulty in response to detection of a threshold number of errors therein after the encoded data block is decoded.

9. A method, comprising:

writing, using M write transducers of a magnetic head, a data set to a sequential access medium, the data set comprising a number of sub data sets of fixed size, each sub data set comprising a plurality of encoded data blocks comprising codewords, each codeword comprising a predetermined number of symbols;

reading, using M read transducers of the magnetic head, the data set in a read-while-write process to identify faulty encoded data blocks, each of the faulty encoded data blocks comprising at least one faulty codeword;

selecting a particular logical track from a predetermined subset of logical tracks in a rewrite area of the sequential access medium to rewrite the faulty encoded data blocks, the rewrite area being positioned subsequent to a position of the data set on the sequential access medium, wherein the predetermined subset of logical tracks includes D1+D2+1 logical tracks, and wherein 0<

D1+D2<

M/4; and

rewriting a correct version of a first of the encoded data blocks identified as faulty in a first encoded data block set to the rewrite area of the sequential access medium, wherein only one encoded data block from a particular sub data set is rewritten in a single encoded data block set in the rewrite area.

10. The method as recited in claim 9, wherein each of the symbols are 10 bits in size, the method further comprising:

selecting a second logical track from the predetermined subset of logical tracks in the rewrite area of the sequential access medium; and

rewriting a correct version of a second of the faulty encoded data blocks within the first encoded data block set to the second logical track in response to the first encoded data block being from a different sub data set than the second of the encoded data blocks.

11. The method as recited in claim 9, wherein each of the predetermined subsets of logical tracks comprises three logical tracks in sequence corresponding to D1=1 and D2=1.

12. The method as recited in claim 9, wherein each of the predetermined subsets of logical tracks comprises five logical tracks in sequence corresponding to D1=2 and D2=2.

13. The method as recited in claim 9, wherein each encoded data block is written to the sequential access medium as four symbol-interleaved Reed-Solomon RS(240,228) C1 codewords over a Galois Field GF(256).

14. The method as recited in claim 9, wherein each encoded data block is written to the sequential access medium as two symbol-interleaved Reed-Solomon RS(384,364) C1 codewords over a Galois Field GF(1024).

15. The method as recited in claim 9, wherein each encoded data block is written to the sequential access medium as one Reed-Solomon RS(768,728) C1 codeword over a Galois Field GF(1024).

16. The method as recited in claim 9, further comprising decoding the data set read from the sequential access medium to determine the faulty encoded data blocks, wherein an encoded data block is determined to be faulty in response to detection of a threshold number of errors therein after the encoded data block is decoded.

17. A computer program product, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the embodied program instructions being executable by a processor to cause the processor to:

write, by the processor using M write transducers of a magnetic head, a data set to a sequential access medium, the data set comprising a number of sub data sets of fixed size, each sub data set comprising a plurality of encoded data blocks comprising codewords, each codeword comprising a predetermined number of symbols;

read, by the processor using M read transducers of the magnetic head, the data set in a read-while-write process to identify faulty encoded data blocks, each of the faulty encoded data blocks comprising at least one faulty codeword;

select, by the processor, a particular logical track from a predetermined subset of logical tracks in a rewrite area of the sequential access medium to rewrite the faulty encoded data blocks, the rewrite area being positioned subsequent to a position of the data set on the sequential access medium, wherein the predetermined subset of logical tracks includes D1+D2+1 logical tracks, and wherein 0<

D1+D2<

M/4; and

rewrite, by the processor, a correct version of a first of the encoded data blocks identified as faulty in a first encoded data block set to the rewrite area of the sequential access medium, wherein only one encoded data block from a particular sub data set is rewritten in a single encoded data block set in the rewrite area.

18. The computer program product as recited in claim 17, wherein each of the symbols are 8 bits in size, and wherein each encoded data block is written to the sequential access medium as four symbol-interleaved Reed-Solomon RS(240,228) C1 codewords over a Galois Field GF(256).

19. The computer program product as recited in claim 17, wherein each of the predetermined subsets of logical tracks comprise three to five logical tracks in sequence corresponding to D1=1 and D2=1.

20. The computer program product as recited in claim 17, wherein the embodied program instructions are further executable by the processor to cause the processor to:

select, by the processor, a second logical track from the predetermined subset of logical tracks in the rewrite area of the sequential access medium; and

rewrite, by the processor, a correct version of a second of the faulty encoded data blocks within the first encoded data block set to the second logical track in response to the first encoded data block being from a different sub data set than the second of the encoded data blocks.