Patent ID: 8289641

Claim:
A method reducing the risk of data becoming unrecoverable in a data storage system including a plurality of data storage devices, each data storage device having a plurality of physical blocks to which data is written to in write operations and from which data is read in read operations, each data storage device having a plurality of block groups each associated with a subset of the plurality of physical blocks, the method comprising: recognizing read errors occurring in response to read operations; associating one of the block groups with each read error; counting the number of read errors associated with each block group; determining any one block group to be faulty when the counted number of read errors for that any one block group exceeds a predetermined threshold value, the data storage device having the block group determined to be faulty constituting a partially failed data storage device; and upon determining any one block group of any one of the plurality of data storage devices to be faulty: copying data from data blocks of non-faulty block groups of the partially failed data storage device to at least one of the other data storage devices within the data storage system; and restoring data that was previously stored in data blocks of the block group determined to be faulty on the partially failed data storage device to at least one of the other data storage devices within the data storage system, the data restored not being copied directly from the block group determined to be faulty.