# US 8,786,972 B2 · Magnetic recording disk drive with method for recovery of data from failed data sectors

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- Number: US 8,786,972 B2
- Document ID: US8786972B2
- Status: Granted
- Kind: B2
- Application number: 13/680,087
- Filed: 2012-11-18
- Published: 2014-05-22
- Granted: 2014-07-22
- Earliest claimed: 2012-11-18
- Assignees: HGST Netherlands B.V.
- Applicants: HGST Netherlands B.V.
- Inventors: Michael Konrad Grobis; Kurt Allan Rubin
- Web page: https://patentgrep.com/patent/US8786972B2

## CPC

- G11B 20/1889: {with discs}
- G11B 20/182: {using test patterns}
- G11B 20/1833: {by adding special lists or symbols to the coded information (G11B20/1806, G11B20/1866 take precedence)}
- G11B 2020/1836: {using a Reed Solomon [RS] code}
- G11B 2020/185: {using an low density parity check [LDPC] code}
- G11B 2220/252: Patterned or quantised magnetic media, i.e. bits are stored in predefined single domain elements
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

A magnetic recording disk drive determines the locations of defective bits in a failed data sector, and allows for the error correction code (ECC) to correctly decode the data from the sector. After a sector has failed decoding, the digitized waveform and the read channel state from the failed sector are stored in memory. A nondata pattern is written to the failed sector and read back to determine the locations of the defective data bits in the failed sector, which are then used to update the read channel state. The data pattern from the failed sector, with the identified bit error locations, is attempted to be decoded. If the decoding is successful then the sector is marked as bad and the correctly decoded data pattern is written to a different region of the disk, for example physical sectors specifically intended for use as spare sectors.

## Claims

### Claim 1

A magnetic recording disk drive comprising:
a magnetic recording disk having a recording surface with a plurality of circular data tracks containing data sectors, the data sectors containing magnetizable data regions, each data region representing a data bit;
a write head associated with said disk surface for writing desired data patterns in the sectors by generating a magnetic write field to magnetize the data regions;
a read head for detecting the magnetic state of the data regions in the sectors;
a detector coupled to the read head for detecting the magnetic state of the data regions into data patterns of data bits;
an error corrector for correcting bit errors in the detected data patterns;
a controller for synchronizing the reading and writing of data to individual data regions; and
memory coupled to the controller and containing a program of instructions readable by the controller for recovering data written to data sectors containing defective data regions, the program of instructions undertaking the method acts comprising:
(a) determining that a data pattern in a sector cannot be corrected by the error corrector;
(b) storing in memory the uncorrectable data pattern;
(c) writing a predetermined nondata pattern to the sector containing said uncorrectable data pattern;
(d) reading said written predetermined nondata pattern;
(e) identifying the location of defective data regions in said sector that cannot be corrected by comparing the read predetermined nondata pattern with the written predetermined nondata pattern;
(f) attempting to correct, with the error corrector, said data pattern that cannot be corrected by marking bits representing the identified defective data regions as hard bit errors; and
if at step (f) said data pattern can be corrected, writing the corrected data pattern to a different sector and then marking the sector for said data pattern as bad.

### Claim 2 (depends on 1)

The method of claim 1 further comprising verifying that the uncorrectable data pattern stored in memory matches the uncorrectable data pattern in the sector.

### Claim 3 (depends on 1)

The disk drive of claim 1 wherein the predetermined nondata pattern is a first pattern and the method acts further comprise:
if at step (e) the number of defective data regions exceeds a predetermined threshold, wherein said predetermined threshold is a multiple of the maximum number of errors that can be reliably decoded by the error corrector, repeating steps (c) through (f) with a second predetermined nondata pattern.

### Claim 4 (depends on 3)

The method of claim 3 where the second predetermined nondata pattern is different from said first pattern.

### Claim 5 (depends on 1)

The disk drive of claim 1 wherein the method acts further comprise:
if at step (e) the number of defective data regions exceeds a predetermined threshold, wherein said predetermined threshold is a multiple of the maximum number of errors that can be reliably decoded by the error corrector, repeating step (c) by writing said predetermined nondata pattern with a write clock phase shift.

### Claim 6 (depends on 1)

The disk drive of claim 1 further comprising verifying that the corrected data is written correctly.

### Claim 7 (depends on 1)

The disk drive of claim 1 wherein the method acts further comprise:
storing in memory the data patterns from sectors radially adjacent to the sector that contains the uncorrectable data pattern; and
if at step (f) said data pattern can be corrected, then recalling from memory said data patterns from said radially adjacent sectors and writing said data patterns from said radially adjacent sectors back to said radially adjacent sectors.

### Claim 8 (depends on 1)

The disk drive of claim 1 wherein the error corrector is a Reed-Solomon error corrector for correcting bit errors by correcting symbols containing a grouping of data bits, and wherein step (f) comprises attempting to correct, with the error corrector, said data pattern that cannot be corrected by marking symbols containing the identified defective data islands as unreliable.

### Claim 9 (depends on 1)

The disk drive of claim 1 wherein the error corrector is a low-density-parity-check (LDPC) error corrector for correcting bit errors by correcting states containing a grouping of data bits, and wherein step (f) comprises attempting to correct, with the error corrector, said data pattern that cannot be corrected by marking states containing the identified defective data islands as unreliable.

### Claim 10 (depends on 1)

The disk drive of claim 1 wherein the recording surface of the disk is a continuous-media magnetic recording surface.

### Claim 11 (depends on 1)

The disk drive of claim 1 wherein the magnetic recording disk is a bit-patterned-media (BPM) disk and wherein the data regions are discrete data islands.

### Claim 12 (depends on 1)

The disk drive of claim 1 wherein the disk drive is a heat-assisted magnetic recording (HAMR) disk drive.

### Claim 13 (depends on 1)

The disk drive of claim 1 wherein the disk drive is a shingled magnetic recording (SMR) disk drive.

### Claim 14

A bit-patterned-media (BPM) magnetic recording disk drive comprising:
a magnetic recording disk having a recording surface with a plurality of circular data tracks containing data sectors, the data sectors containing discrete magnetizable data islands;
a write head associated with said disk surface for writing desired data patterns in the sectors by generating a magnetic write field to magnetize the data islands;
a read head for detecting the magnetic state of the data islands in the sectors;
a detector coupled to the read head for detecting the magnetic state of the data islands into data patterns of data bits;
an error corrector for correcting bit errors in the detected data patterns;
a controller for synchronizing the reading and writing of data to individual data islands; and
memory coupled to the controller and containing a program of instructions readable by the controller for recovering data written to data sectors containing defective data islands, the program of instructions undertaking the method acts comprising:
(a) determining that a data pattern in a sector cannot be corrected by the error corrector;
(b) storing in memory the uncorrectable data pattern;
(c) writing a predetermined nondata pattern to the sector containing said uncorrectable data pattern;
(d) reading said written predetermined nondata pattern;
(e) identifying the location of defective data islands in said sector that cannot be corrected by comparing the read predetermined nondata pattern with the written predetermined nondata pattern; and
(f) attempting to correct, with the error corrector, said data pattern that cannot be corrected by marking bits representing the identified defective data islands as hard bit errors; and
if at step (e) the number of defective data islands exceeds a predetermined threshold, wherein said predetermined threshold is a multiple of the maximum number of errors that can be reliably decoded by the error corrector, repeating step (c) by one of writing said predetermined nondata pattern with a write clock phase shift and writing a second predetermined pattern different from said first pattern, and then repeating steps (d) through (f).

### Claim 15 (depends on 14)

The disk drive of claim 14 wherein the method acts further comprise:
if at step (f) said data pattern can be corrected, then marking the sector for said data pattern as bad, and writing the corrected data pattern to a different sector.

### Claim 16 (depends on 15)

The disk drive of claim 15 wherein the method acts further comprise:
storing in memory the data patterns from sectors radially adjacent to the sector that contains the uncorrectable data pattern; and
if at step (f) said data pattern can be corrected, then recalling from memory said data patterns from said radially adjacent sectors and writing said data patterns from said radially adjacent sectors back to said radially adjacent sectors.