Partial mirroring during expansion thereby eliminating the need to track the progress of stripes updated during expansion

Abstract

A method, system and computer program product for performing an expansion of a disk array. Upon the failure of a disk in the disk array, the failed disk may be rebuilt stripe by stripe in the spare units distributed among other disks in the disk array. Upon repairing or replacing the failed disk with a spare disk, the repaired or spare disk may be rebuilt stripe by stripe using the data from the spare units. Upon receiving a write request to a stripe unit that has been rebuilt in the repaired or spare disk during expansion, the data of the request may be written in the stripe unit requested. Further, the data written may be mirrored, i.e., copied and stored, in the spare unit corresponding to the stripe unit requested. By mirroring the data to the corresponding spare unit, tracking each stripe that was updated during expansion may be eliminated.