High availability is attained by rebuilding the contents of a failed disk on a spare disk or areas.
Dedicated, distributed, and parity sparing approaches for rebuild are considered and various rebuild options are described. Single block writes prevalent with OLTP result in the small write penalty wrt nonRAID systems. The last solution allows the deferral of updates, so that destaging of data to disk is carried out with lower priority than disk reads. Repeated updates of dirty blocks in NVS and grouping destages may result in significant destage efficiency. The response time for fork-join requests to reconstruct data blocks is obtained via interpolation between lower and upper bounds.