Almost complete address translation (ACATS) disk array declustering

We present a novel declustering scheme (ACATS) for reliability stripes in an orthogonal disk array. Our scheme is deterministic, run-time efficient, and provides frequently the best possible and always an almost best possible distribution of failure-induced incremental rebuild workloads. Our scheme provides protection against single disk as well as single string failures within the disk array. Our approach presents a framework in which the Level 5 RAID organization logically appears as a Level 4 RAID; it facilitates the provision of distributed sparing in exactly the same manner. ACATS does not require the existence of a suitably configured block design or of a run-time efficient pseudo-random number generator; it is applicable to arbitrarily configured orthogonal disk arrays. Our scheme is faster than declustering schemes that use pseudo-random permutations and achieves better uniformity of disk loads during a disk rebuild; it is simpler than schemes based on block designs. ACATS provides a rich spectrum of declustering schemes.