Method and apparatus with improved error correction and error information availability

For use with a multiple level error correction code format, apparatus for correcting errors in encoded uncorrected data in a disk storage device operative in a deferred mode to pass error correction information to a storage director, said apparatus comprising:

• syndrome generating means for receiving the uncorrected data and generating in the storage device first and second level syndromes therefrom;
• means, including decoder means, resident in the storage device, for decoding the syndromes to provide first and second level error pattern and location information;
• means, resident in the storage device, for adjusting the second level syndromes to reflect and retain the first level error pattern and location information;
• and
• means for transmitting said information to the storage director for completion of the first level of correction and performance of subsequent levels of correction.

A method of correcting errors in encoded uncorrected data in a disk storage device, using a multiple level error correction code formatted into a block containing a number of subblocks, said method comprising the steps of:

• (a) selecting between deferred mode error correction or on-the-fly mode error correction;
• and
• (b) during deferred mode operation:
• (i) transmitting the uncorrected data to a storage director and concurrently generating in the storage device first and second level syndromes from the uncorrected data,
• (ii) decoding the first level syndromes to provide first level error pattern and location information;
• (iii) adjusting the second level syndromes to reflect the first level error pattern and location information;
• and
• (iv) after all uncorrected data has been received by the storage director, transmitting said information to the storage director for completion of the first level of correction and performance o subsequent levels of correction;
• and
• (c) during on-the-fly mode operation:
• (i) transmitting the uncorrected data to a buffer and concurrently generating in the storage device first and second level syndromes from the uncorrected data;
• (ii) decoding the first level syndromes to provide error pattern information;
• (iii) adjusting the second level syndromes to reflect first level error pattern and location information;
• (iv) after a delay time corresponding to the time necessary to read out the next subblock, exclusive OR'ing the buffered uncorrected data with the first level error pattern information to provide data with the first level of error correction completed;
• and
• (v) transmitting the first level corrected data to the storage director for completion of subsequent levels of correction.

For use with a two-level error correction code formatted into a block comprising a number of subblocks, apparatus for correcting errors in encoded uncorrected data in a disk storage device operatively connected to a storage director, said apparatus comprising:

• means for selectively conditioning the apparatus for deferred mode or on-the-fly error correction;
• means, including syndrome generating means and decoder means, resident in the storage device for decoding syndromes from the uncorrected data to provide error pattern and displacement information;
• means, resident in the storage device, for adjusting the second level syndromes to reflect the first level error pattern and displacement information;
• means operative when conditioned for deferred mode operation for transmitting said error pattern and displacement information to the storage director at the end of reading of the block for completion of the first level of correction and performance of the second level of correction;
• buffer means operative when conditioned for on-the-fly operation for storing the uncorrected data;
• means operative when conditioned for on-the-fly operation for exclusive OR'ing the buffered uncorrected data, after a delay time corresponding to the time necessary to read out the next subblock, with the error pattern information for outputting data with the first level of error correction completed;
• and
• means for transmitting the outputted data to the storage director for execution of the second level of correction.