Low latency lateral decoding of data for retrieval from magnetic tape

Patent metadata

Field	Value
Publication number	US-10120599-B2
Application number	US-201615380987-A
Country	US
Kind code	B2
Filing date	Dec 15, 2016
Priority date	Dec 15, 2016
Publication date	Nov 6, 2018
Grant date	Nov 6, 2018

Abstract

In one embodiment, a method includes reading a plurality of narrow-spread (NS) codewords from M tracks of a magnetic tape medium using a plurality of read elements, the plurality of NS codewords collectively comprising data logically organized as a predetermined number of two-dimensional arrays. Each two-dimensional array includes a predetermined number of NS codewords positioned orthogonally to a predetermined number of wide-spread (WS) codewords, with a first NS codeword from a first two-dimensional array being read in its entirety from the magnetic tape medium prior to reading a second NS codeword from the first two-dimensional array. The method also includes laterally decoding each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium in succession prior to decoding any WS codewords from the first two-dimensional array. The NS codewords are protected with a stronger encoding than the WS codewords within each two-dimensional array.

First claim

What is claimed is:

1. A tape drive, comprising:
a plurality of read elements;
a processing circuit; and
logic integrated with the processing circuit, executable by the processing circuit, or integrated with and executable by the processing circuit, the logic being configured to cause the processing circuit to:
read a plurality of narrow-spread (NS) codewords from M tracks of a magnetic tape medium using the plurality of read elements, the plurality of NS codewords collectively comprising data logically organized as a predetermined number of two-dimensional arrays, each two-dimensional array comprising a predetermined number of NS codewords positioned orthogonally to a predetermined number of wide-spread (WS) codewords, wherein a first NS codeword from a first two-dimensional array is read in its entirety from the magnetic tape medium prior to reading a second NS codeword from the first two-dimensional array; and
laterally decode each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium in succession prior to decoding any WS codewords from the first two-dimensional array,
wherein the predetermined number of NS codewords within each two-dimensional array are protected with a stronger encoding than the predetermined number of WS codewords within each two-dimensional array.

2. The tape drive as recited in claim 1 , wherein the stronger encoding is based on a higher correctable percentage of erroneous symbols in a NS codeword as compared to a correctable percentage of erroneous symbols in a WS codeword.

3. The tape drive as recited in claim 1 , wherein the stronger encoding is based on T2/N2 being greater than T1/N1, wherein T1 equals floor (P1/2), N1 equals a length of a WS codeword, P1 is a WS codeword parity length and equals the WS codeword length minus a WS data word length, and wherein T2 equals floor (P2/2), N2 equals a length of a NS codeword, P2 is a NS codeword parity length and equals the NS codeword length minus a NS data word length.

4. The tape drive as recited in claim 3 , wherein more than one symbol of the first NS codeword from the first two-dimensional array is read from each of the M tracks of the magnetic tape medium, and wherein a WS codeword stored to the magnetic tape medium occupies at least (N1−1) times as much distance on the magnetic tape medium in a longitudinal direction than a NS codeword stored to the magnetic tape medium.

5. The tape drive as recited in claim 1 , wherein the logic further causes the processing circuit to:
reiterate the lateral decoding of each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium and decoding of each WS codeword from the first two-dimensional array.

6. The tape drive as recited in claim 1 , wherein the logic further causes the processing circuit to:
perform one or more digital front-end (DFE) functions on each of the M tracks of data read from the magnetic tape medium on a per-channel basis prior to laterally decoding each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium; and
perform soft detection on each of the M tracks of data read from the magnetic tape medium on the per-channel basis prior to laterally decoding each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium,
wherein bit decisions from performance of the soft detection are used in a first pass of performing the one or more DFE functions, and
wherein bit decisions from the lateral decoding of each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium are used in each subsequent pass of performing the one or more DFE functions.

7. The tape drive as recited in claim 6 , wherein the one or more DFE functions are selected from a group comprising: asymmetry cancellation, adaptive equalization, timing control, and gain adjustment.

8. The tape drive as recited in claim 1 , wherein the logic further causes the processing circuit to:
perform soft detection on each of the M tracks of data read from the magnetic tape medium on a per-channel basis prior to laterally decoding each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium,
wherein bit decisions from performance of the soft detection are used in each pass of performing one or more digital front-end (DFE) functions on each of the M tracks of data read from the magnetic tape medium subsequent to a first pass.

9. A method, comprising:
reading a plurality of narrow-spread (NS) codewords from M tracks of a magnetic tape medium using a plurality of read elements, the plurality of NS codewords collectively comprising data logically organized as a predetermined number of two-dimensional arrays, each two-dimensional array comprising a predetermined number of NS codewords positioned orthogonally to a predetermined number of wide-spread (WS) codewords, wherein a first NS codeword from a first two-dimensional array is read in its entirety from the magnetic tape medium prior to reading a second NS codeword from the first two-dimensional array; and
laterally decoding each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium in succession prior to decoding any WS codewords from the first two-dimensional array,
wherein the predetermined number of NS codewords within each two-dimensional array are protected with a stronger encoding than the predetermined number of WS codewords within each two-dimensional array.

10. The method as recited in claim 9 , wherein the stronger encoding is based on a higher correctable percentage of erroneous symbols in a NS codeword as compared to a correctable percentage of erroneous symbols in a WS codeword.

11. The method as recited in claim 9 , wherein the stronger encoding is based on T2/N2 being greater than T1/N1, wherein T1 equals floor (P1/2), N1 equals a length of a WS codeword, P1 is a WS codeword parity length and equals the WS codeword length minus a WS data word length, and wherein T2 equals floor (P2/2), N2 equals a length of a NS codeword, P2 is a NS codeword parity length and equals the NS codeword length minus a NS data word length.

12. The method as recited in claim 11 , wherein more than one symbol of each NS codeword is read from each of the M tracks of the magnetic tape medium, and wherein a WS codeword stored to the magnetic tape medium occupies at least (N1−1) times as much distance on the magnetic tape medium in a longitudinal direction than a NS codeword stored to the magnetic tape medium.

13. The method as recited in claim 9 , further comprising:
reiterating the lateral decoding of each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium and decoding of each WS codeword from the first two-dimensional array.

14. The method as recited in claim 9 , further comprising:
performing one or more digital front-end (DFE) functions on each of the M tracks of data read from the magnetic tape medium on a per-channel basis prior to laterally decoding each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium; and
performing soft detection on each of the M tracks of data read from the magnetic tape medium on the per-channel basis prior to laterally decoding each NS codeword from the first two-dimensional array read from the M tracks of the magnetic tape medium,
wherein bit decisions from performance of the soft detection are used in a first pass of performing the one or more DFE functions, and
wherein bit deci

Assignees

• IBM

Inventors

• Cideciyan Roy D
• Furrer Simeon
• Gale Ernest S
• Lantz Mark A

Classifications

• G06F3/064

  Management of blocks · CPC title

• G11B2020/1853

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

• H03M13/27

  using interleaving techniques · CPC title

• H03M13/2909

  Product codes · CPC title

• G06F11/1076

  Parity data used in redundant arrays of independent storages, e.g. in RAID systems · CPC title