Seagate Technology Incorporated

Maxtor Corporation

Rajita Shrestha

James C Alexander

Michael H Chen

Lace J Herman

Jerry Moline

Christine Green

Dave Rewerts

Chris Aumann

Glen Rewerts

Systems for identifying potentially erroneous and/or erased data are provided. Systems have a bit detector, an accumulator, and a data reconstruction processor. The bit detector assigns values to bits read in a data signal. The bit detector illustratively assigns multiple values to each of the bits. The accumulator accumulates a count of the multiple values assigned by the bit detector for each of the bits. The accumulator associates each bit with a particular value based at least in part on its accumulated count. The data reconstruction processor determines for each of the bits a confidence level of the particular value associated to it. The data reconstruction process sets flags for a portion of the bits. The flags identify the portion of the bits as possible erased or erroneous data. The flags are set based at least in part on the confidence levels of the portion of the bits.

Identification of potentially erroneous and/or erased data

A system for enhancing the error correction capability of an error correction code ('ECC') during error recovery operations accumulates, for respective bits, counts of the number of times the bits are detected as 1s in multiple re-reads of a data signal. The system then determines, based on the associated count, if a reconstructed bit should be considered a 1 or 0, or neither, that is, if the reconstructed bit should be considered erroneous, by comparing the count to a majority detection threshold and then to either an upper or a lower predetermined threshold that corresponds to the confidence with which the bit is reconstructed as a either a 1 or a 0. If the confidence is sufficiently low, that is, if the count falls below the upper threshold or above the lower threshold, the reconstructed bit is flagged as erroneous. After all of the bits are reconstructed, the system groups the bits into symbols to reproduce the ECC codeword, and sets erasure pointers that identify the locations of a predetermined number, s, of the symbols that are associated with the highest degree of uncertainty, that is, the largest numbers of flagged bits or, as appropriate, the largest numbers of flagged bits with the lowest confidence levels. The error correction operation then decodes the symbols in the identified locations as erasures. The system, using an (n, k) distance d Reed-Solomon ECC uses 2t=n&#x2212;k redundancy symbols to correct the s erasures and up to errors.

Majority-detected erasure enhanced error correction

Data recovery, following a read error in a hard disk drive, is provided which includes an adjustment of fly height. In one embodiment, some re-reads are performed by both adjusting the fly height and the off-track positioning of the read head. In one embodiment, two or more fly heights are normally used during read/write operations such as in a zoned manner, and adjustments to fly heights are performed with respect to the fly height for the zone where the error occurred.

Hard disk drive fly height adjust method and apparatus during error recovery

An off-track error recovery method and apparatus for a disk drive are disclosed herein. Off-track errors are either due to vibration of the disk drive or due to defective servo data stored on a disk surface of the disk drive. In order to tailor error recovery operations associated with each of the two types of off-track errors, the present invention distinguishes between the two types of errors, when possible. Accordingly, the overall time for performing off-track error recovery operations is reduced and/or off-track error recovery operations are made more efficient.

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Westminster, CO, United States of America

Rajita Shrestha