A technique for managing mirrored disks

Disk mirroring is a highly effective technique for improving the fault tolerance and performance of storage systems. Mirroring requires that those disks holding the current data must be determined when recovering from total system failure. In a two disk system, this is only a minor problem since the operator can indicate which disk is current. The complexity increases when more disks are introduced, and requiring human intervention is impractical when the target environment is the consumer market. In these situations, automatic recovery must be used when possible. We describe an efficient algorithm for managing the consistency of mirrored storage. Our algorithm requires only n+log n bits of state per disk and does not require logging or quorum collection.