Track-dependent decoding

Patent metadata

Field	Value
Publication number	US-9837117-B2
Application number	US-201615179789-A
Country	US
Kind code	B2
Filing date	Jun 10, 2016
Priority date	Nov 19, 2015
Publication date	Dec 5, 2017
Grant date	Dec 5, 2017

Abstract

In one embodiment, a method includes reading, using a plurality of read sensors of a magnetic head in a read channel of a tape drive, encoded data from a plurality of tracks of a magnetic tape medium simultaneously. Also, the method includes monitoring statistics for the read channel, the statistics monitored for the read channel including exponentially averaged mean squared error (MSE) or signal-to-noise ratio (SNR) for each simultaneously read track. Moreover, the method includes performing track-dependent erasure decoding on the encoded data based on detection of one or more time-varying signal quality issues associated with at least one of the plurality of tracks read simultaneously from the magnetic tape medium. The one or more time-varying signal quality issues are determined based on side information about reliability of detected bytes within C1 codewords of each simultaneously-read track.

First claim

What is claimed is:

1. A method, comprising:
performing track-dependent erasure decoding on encoded data based on detection of one or more time-varying signal quality issues associated with at least one of a plurality of tracks read simultaneously from a data storage medium.

2. The method as recited in claim 1 , wherein the one or more time-varying signal quality issues is determined based on side information about reliability of detected bytes within C1 codewords of each simultaneously-read track, and wherein the side information further comprises read or write channel performance of at least one read or write channel falling below a predetermined threshold based on statistics monitored by firmware of a tape drive used to read the plurality of tracks.

3. The method as recited in claim 2 , wherein the side information comprises C1 decoder performance falling below a predetermined threshold based on statistics accumulated for the C1 decoder during C1 decoding of the encoded data, and wherein the statistics accumulated for the C1 decoder comprise a number of uncorrectable C1 codewords for each track.

4. The method as recited in claim 3 , wherein the side information is selected from the group consisting of:
C1 decoder performance falling below the predetermined threshold for a specific track in response to detection of at least one uncorrectable C1 codeword read from the specific track;
C1 decoder performance falling below the predetermined threshold for a specific track in response to detection of more than a predetermined number (N) of uncorrectable C1 codewords within a preset number (M) of most recently decoded C1 codewords for the specific track; and
a number of run-length limited (RLL) error detection flags per C1 codeword, wherein track-dependent erasure decoding is performed on the encoded data for a specific track in response to a determination of more than an allowable number of RLL error detection flags in a single C1 codeword read from the specific track.

5. The method as recited in claim 1 , further comprising monitoring statistics for a read channel of a tape drive used to read the plurality of tracks, the statistics monitored for the read channel including exponentially averaged mean squared error (MSE) or signal-to-noise ratio (SNR) for each simultaneously read track.

6. The method as recited in claim 1 , wherein the performing track-dependent erasure decoding on the encoded data further comprises:
calculating an erasure coefficient for each byte in a particular C1 codeword read using a specific track, each erasure coefficient being a measure of a reliability of an associated decoded byte;
summing all erasure coefficients for the particular C1 codeword to produce a sum of erasure coefficients;
determining whether the sum of erasure coefficients is greater than a predetermined configurable coefficient threshold; and
performing track-dependent erasure decoding on the encoded data for the specific track in response to a determination that the sum is greater than the predetermined configurable threshold.

7. The method as recited in claim 1 , wherein the performing track-dependent erasure decoding on the encoded data further comprises:
performing C1 decoding of the encoded data to produce a plurality of C1 codewords;
determining a probability that any of the plurality of C1 codewords individually includes a number of C1 byte errors that exceeds a predetermined threshold of C1 byte errors;
enabling erasure pointers for C2 decoding in response to a determination that the probability is greater than a threshold probability;
inserting an erasure pointer in place of each C1 codeword of the plurality of C1 codewords for which the probability is greater than the threshold probability to produce a plurality of erasure-enabled C1 codewords; and
performing C2 decoding on the plurality of erasure-enabled C1 codewords using C2 error-and-erasure decoding.

8. The method as recited in claim 7 , wherein erasure pointers are enabled only on a set of tracks having a highest relative probability that a C1 codeword read from that track includes C1 byte errors exceeding the predetermined threshold of C1 byte errors.

9. 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:
perform, by the processor, track-dependent erasure decoding on encoded data based on detection of one or more time-varying signal quality issues associated with at least one of a plurality of tracks read simultaneously from a data storage medium.

10. The computer program product as recited in claim 9 , wherein the one or more time-varying signal quality issues is determined based on side information about reliability of detected bytes within C1 codewords of each simultaneously-read track, and wherein the side information further comprises read or write channel performance of at least one read or write channel falling below a predetermined threshold based on statistics monitored by firmware of a tape drive used to read the plurality of tracks.

11. The computer program product as recited in claim 10 , wherein the side information comprises C1 decoder performance falling below a predetermined threshold based on statistics accumulated for the C1 decoder during C1 decoding of the encoded data, and wherein the statistics accumulated for the C1 decoder comprise a number of uncorrectable C1 codewords for each track.

12. The computer program product as recited in claim 11 , wherein the side information is selected from the group consisting of:
C1 decoder performance falling below the predetermined threshold for a specific track in response to detection of at least one uncorrectable C1 codeword read from the specific track;
C1 decoder performance falling below the predetermined threshold for a specific track in response to detection of more than a predetermined number (N) of uncorrectable C1 codewords within a preset number (M) of most recently decoded C1 codewords for the specific track; and
a number of run-length limited (RLL) error detection flags per C1 codeword, wherein track-dependent erasure decoding is performed on the encoded data for a specific track in response to a determination of more than an allowable number of RLL error detection flags in a single C1 codeword read from the specific track.

13. The computer program product as recited in claim 9 , wherein the program instructions are further executable by the processor to cause the processor to monitor, by the processor, statistics for a read channel of a tape drive used to read the plurality of tracks, the statistics monitored for the read channel including exponentially averaged mean squared error (MSE) or signal-to-noise ratio (SNR) for each simultaneously read track.

14. The computer program product as recited in claim 9 , wherein the program instructions executable by the processor to cause the processor to perform track-dependent erasure decoding on the encoded data further cause the processor to:
calculate, by the processor, an erasure coefficient for each byte in a particular C1 codeword read using a specific track, each erasure coefficient being a measure of a reliability of an associated decoded byte;
sum, by the processor, all erasure coefficients for the particular C1 codeword to produce a sum of erasure coefficients;
determine, by the processor, whether the sum of erasure coefficients is greater than a predetermined configurable coefficient threshold; and
perform, by the processor, track-dependent erasure decoding

Assignees

• IBM

Inventors

• Bentley Steven R
• Cideciyan Roy D
• Furrer Simeon
• Tanaka Keisuke

Classifications

• G11B2020/10898

  Overwriting or replacing recorded data · CPC title

• G11B2020/1853

  using a product code which has inner and outer parity symbols · CPC title

• G11B20/1833 Primary

  by adding special lists or symbols to the coded information (G11B20/1806, G11B20/1866 take precedence) · CPC title

• G11B5/00826

  comprising a plurality of single poles or gaps or groups thereof operative at the same time · CPC title

• G11B20/1816 Primary

  Testing · CPC title