System and method for calculating RAID 6 check codes

A system for updating RAID 6 check codes by transforming a first check symbol difference to a second check symbol difference comprising:

• means for establishing a generator polynomial of the form G=X.sup.N +X.sup.D +1;
• means for selecting an index K;
• means for renumbering said first check symbol difference by K bits to define a renumbered check symbol difference;
• means for calculating a logical difference of each of said first K bits of said renumbered check symbol difference with each of another K bits of said renumbered check symbol difference starting at bit position D within said renumbered check symbol difference thereof forming a resultant K bits of said renumbered check symbol difference;
• and
• means for defining said second check symbol difference by said renumbered check symbol difference inclusive of said resultant K bits thereof.

A computer system including a RAID 6 storage array comprising a plurality of physical storage devices for storing data symbols and first and second check symbols for reconstructing said data symbols thereon, said computer system further comprising a data processor for recomputing said first and second check symbols in response to changes in said data symbols, said computer system comprising:

• means for determining first check symbol differences in response to changes in said data symbols;
• means for updating said first check symbols based upon said first check symbol differences;
• means for establishing a generator polynomial of the form G=X.sup.N +X.sup.D +1;
• means for selecting an index K;
• means for renumbering said first check symbol differences by K bits to define renumbered check symbol differences;
• means for calculating a logical difference of each of said first K bits of each of said renumbered check symbol differences with each of another K bits of said renumbered check symbol differences starting at bit position D within said renumbered check symbol differences thereof forming a resultant K bits of said renumbered check symbol differences starting at bit position D;
• means for defining said second check symbol differences by said renumbered check symbol differences inclusive of said resultant K bits;
• means for updating said second check symbols based upon said second check symbol differences;
• means for writing said changed data symbols and said first and second check symbols to said storage array.