Efficient rewrite using larger codeword sizes

Patent metadata

Field	Value
Publication number	US-10418062-B2
Application number	US-201715847774-A
Country	US
Kind code	B2
Filing date	Dec 19, 2017
Priority date	Dec 19, 2017
Publication date	Sep 17, 2019
Grant date	Sep 17, 2019

Abstract

In one embodiment, a method includes writing a data set to a sequential access medium. The method also includes reading the data set immediately after being written to the sequential access medium in a read-while-write process to identify one or more faulty encoded data blocks, each of the one or more faulty encoded data blocks including at least one faulty codeword having symbols at least 10 bits in size. Moreover, the method includes rewriting a first of the one or more faulty encoded data blocks within a first encoded data block set to a particular logical track in 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 faulty encoded data block from a particular sub data set is rewritten in a single encoded data block set in the rewrite area.

First claim

What is claimed is:

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 plurality of M 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 in an interleaved or non-interleaved arrangement, each codeword comprising a predetermined number of symbols having a size of at least 8 bits for each symbol;
read, using the plurality of M read transducers, the data set immediately after being written to the sequential access medium in a read-while-write process to identify one or more faulty encoded data blocks, each of the one or more 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 first written 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 first of the one or more faulty encoded data blocks within a first encoded data block set to the particular logical track in the rewrite area of the sequential access medium, wherein only one faulty 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 second of the one or more faulty encoded data blocks within the first encoded data block set to the second logical track in response to the first of the one or more faulty encoded data blocks being from a different sub data set than the second of the one or more faulty 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 one or more 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 a plurality of at least 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 in an interleaved or non-interleaved arrangement, each codeword comprising a predetermined number of symbols having a size of at least 8 bits for each symbol;
reading, using a plurality of at least M read transducers of the magnetic head, the data set immediately after being written to the sequential access medium in a read-while-write process to identify one or more faulty encoded data blocks, each of the one or more 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 first written 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 first of the one or more faulty encoded data blocks within a first encoded data block set to the particular logical track in the rewrite area of the sequential access medium, wherein only one faulty 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 second of the one or more faulty encoded data blocks within the first encoded data block set to the second logical track in response to the first of the one or more faulty encoded data blocks being from a different sub data set than the second of the one or more faulty 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 one or more 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 a plurality of at least 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 plurali

Assignees

• IBM

Inventors

• Cideciyan Roy D
• Furrer Simeon
• Lantz Mark A

Classifications

• H03M13/1515

  Reed-Solomon codes · CPC title

• H03M13/27

  using interleaving techniques · CPC title

• G11B5/00813

  magnetic tapes · CPC title

• G11B2020/184

  using a cross-interleaved Reed Solomon [CIRC] · CPC title

• G11B20/1886 Primary

  with tapes · CPC title