Locating and correcting corrupt data or syndrome blocks

A method of maintaining consistent data and syndromes in a RAID stripe, comprising:

• reading said RAID stripe, said RAID stripe comprising a plurality of data blocks, a first stored syndrome block, and a second stored syndrome block;
• based on said plurality of data blocks, determining first calculated syndrome block;
• based on said plurality of data blocks, determining a second calculated syndrome block;
• determining a first equality indicator by comparing said first stored syndrome block to said first calculated syndrome block;
• determining a second equality indicator by comparing said second stored syndrome block to said second calculated syndrome block;
• and,
• if said first equality indicator indicates that said first stored syndrome block is not equal to said first calculated syndrome block and if said second equality indicator indicates that said second stored syndrome block is not equal to said second calculated syndrome block, determining at least one suspect block using a method comprising:
• for each one of said plurality of data blocks:
• reconstruct a reconstructed one of said data blocks using said first stored syndrome block;
• determine a reconstructed second syndrome block using said reconstructed one of said data blocks and said plurality of data blocks except said one of said plurality of data blocks;
• determine a suspect block indicator, associated with said one of said data blocks, that indicates whether said second stored syndrome block is equal to said reconstructed second syndrome block;
• and,
• if there is a single one of said plurality of data blocks having an associated suspect block indicator indicating that said second stored syndrome block is equal to said reconstructed second syndrome block, storing said reconstructed one of said data blocks associated with said single one of said plurality of data blocks in said RAID stripe.

A storage system, comprising:

• a plurality of disk drives configured to provide a RAID stripe;
• a RAID processor configured to receive said RAID stripe, said RAID stripe comprising a plurality of data blocks, a first stored syndrome block, and a second stored syndrome block, said RAID processor configured to:
• determine a first calculated syndrome block and a second calculated syndrome block based on said plurality of data blocks;
• determine that said first stored syndrome block and said first calculated syndrome block are not equal, and that said second stored syndrome block and said second calculated syndrome block are not equal;
• determine a reconstructed one of said plurality of data blocks based on said first stored syndrome block and a subset of said plurality of data blocks, said subset of said plurality of data blocks not including a one of said plurality of data blocks,;
• determine a reconstructed second syndrome block based on said subset of said plurality of data blocks and said reconstructed one of said plurality of data blocks;
• and,
• select said one of said plurality of data blocks as said suspect data block based on a determination that said reconstructed second syndrome block and said second stored syndrome block are equal.

A computer readable medium having instructions stored thereon for maintaining consistent data and syndromes in a RAID stripe that, when executed by a computer, at least instruct the computer to:

• read said RAID stripe, said RAID stripe comprising a plurality of data blocks, a first stored syndrome block, and a second stored syndrome block;
• based on said plurality of data blocks, determine a first calculated syndrome block;
• based on said plurality of data blocks, determine a second calculated syndrome block;
• determine a first equality indicator by comparing said first stored syndrome block to said first calculated syndrome block;
• determine a second equality indicator by comparing said second stored syndrome block to said second calculated syndrome block;
• and,
• if said first equality indicator indicates that said first stored syndrome block is not equal to said first calculated syndrome block and if said second equality indicator indicates that said second stored syndrome block is not equal to said second calculated syndrome block, determine at least one suspect block using a method comprising:
• for each one of said plurality of data blocks:
• reconstruct a reconstructed one of said data blocks using said first stored syndrome block;
• determine a reconstructed second syndrome block using said reconstructed one of said data blocks and said plurality of data blocks except said one of said plurality of data blocks;
• determine a suspect block indicator, associated with said one of said data blocks, that indicates whether said second stored syndrome block is equal to said reconstructed second syndrome block;
• and,
• if there is a single one of said plurality of data blocks having an associated suspect block indicator indicating that said second stored syndrome block is equal to said reconstructed second syndrome block, storing said reconstructed one of said data blocks associated with said single one of said plurality of data blocks in said RAID stripe.