Hitachi Global Storage Technologies Netherlands B.v.

Vipul Srivastava

Martin Aureliano Hassner

Kirk Hwang

Nyles Heise

Techniques are provided for performing Galois field arithmetic to detect errors in digital data stored on disks. Two 12-bit numbers or two 10-bit numbers are multiplied together in Galois field using tower arithmetic. In the 12-bit embodiment, a base field GF(2) is first extended to GF(2), GF(2) is extended to a first quadratic extension GF(2), and GF(2) is extended to a second quadratic extension GF(2). In the 10-bit embodiment, the base field GF(2) is first extended to GF(2), and GF(2) is extended to a quadratic extension GF(2). Each of the extensions for the 10-bit and 12-bit embodiments is performed using an irreducible polynomial. All of the polynomials used to generate the first and the second quadratic extensions of the Galois field are in the form x+x+K, where K is an element of the ground field whose absolute trace equals 1.

Techniques for performing reduced complexity galois field arithmetic for correcting errors

Techniques for updating cyclic redundancy check (CRC) bytes for data sectors that have been reassigned to a new logical block address (LBA) are provided. The entire set of CRC check bytes is not recalculated each time that a data sector is reassigned to a new LBA. Instead, only the portion of the CRC check bytes effected by the new LBA are updated. An exclusive OR function is performed on the old LBA and the new reassigned LBA for a data sector. Galois Field multiplication is then performed on the result of the XOR function to generate updated portions of CRC bytes that correspond to the reassigned LBA. An exclusive OR function is then performed on the updated portions of the CRC bytes and the old CRC bytes to generate new CRC bytes.

Error correction/detection code adjustment for known data pattern substitution

Techniques for detecting and correcting burst errors in data bytes formed in a two-level block code structure. A second level decoder uses block level check bytes to detect columns in a two-level block code structure that contain error bytes. The second level decoder generates erasure pointers that identify columns in the two-level block structure effected by burst errors. A first level decoder then uses codeword check bytes to correct all of the bytes in the columns identified by the erasure pointers. The first level decoder is freed to use all of the codeword check bytes only for error byte value calculations. The first level decoder does not need to use any of the codeword check bytes for error location calculations, because the erasure pointers generated by the second level decoder provide all of the necessary error locations. This techniques doubles the error correction capability of the first level decoder.

Techniques for detecting and correcting errors using multiple interleave erasure pointers

Techniques for correcting data bytes on a data storage disk that have been rewritten are provided. A data storage system generates a long block membership (LBM) byte for each sector. The LBM bytes indicates whether the sector is part of a block of sectors. A data storage system can determine whether a failed sector is part of a long block. The data storage system adds the LBM contributions to the CRC and ECC bytes and then attempts to correct the failed sector. If the correction process is successful, the data storage system declares a miscorrection. If the error is not successfully corrected, the data storage system again adds the LBM contributions to the CRC and ECC bytes and then attempts to correct the failed sector. If the correction process is successful, the data correction is accepted if the error pattern and the check byte overlap is greater than a threshold.

Growing community of inventors

San Jose, CA, United States of America

Vipul Srivastava