EVALUATING APPROXIMATELY BALANCED PARITY-DECLUSTERED DATA LAYOUTS FORDISK ARRAYS

Parity-declustered data layouts were developed to reduce the time for on-line failure recovery in disk arrays. They generally require perfec t balancing of reconstruction workload among the disks; this restricti ve balance condition makes such data layouts difficult to construct, I n this paper, we consider approximately balanced data layouts, where s ome variation in the reconstruction workload over the disks is permitt ed. Such layouts are considerably easier to construct than perfectly b alanced layouts, We consider three methods for constructing approximat ely balanced data layouts and analyze their performance both theoretic ally and experimentally. We conclude that on uniform workloads, approx imately balanced layouts have performance nearly identical to that of perfectly balanced layouts.