JOT

Declustering is a well known strategy to achieve maximum I/O parallelism in multi-disk systems. Many declustering methods have been proposed for symmetrical disk sys-tems, i.e, multi-disk systems in which all disks have the same speed and capacity. This work deals with the problem of adapting such declustering methods to work in heteroge-neous environments. In such environments there are many types of disks and servers with a large range of speeds and capacities. We deal first with the case of perfectly declustered queries, i.e., queries which retrieve a fixed pro-portion of the answer from each disk. We propose an algorithm which determines the fraction of the dataset which must, be loaded on each disk. The algorithm may be tailored to find disk loading for minimal re-sponse time for a given da.tabase size, or to compute a system profile showing the optimal loading of the disks for all possible ranges of database sizes