Declustering Databases on Heterogeneous Disk Systems

Declustering is a well known strategy to achieve maximum I/O parallelism in multidisk systems. Many declustering methods have been proposed for symmetrical disk systems, 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 heterogeneous 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 proportion 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 response 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. The support of the Defense Advanced Research Projects Agency, as well as the support of the Department of Energ-y under contract DE-AC03-7GSF00098 is gratefully acknowledged. Permission to copy without fee all OT part of this ,material is granted provided that the copies WY not made OT distributed JOT &eel commercial aavantaye, the VLDB copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission oj the Very Lal-ge Data Base Endowment. To copy otherwise, or to republish, requires a fee d/oT special permission from the Endowment. Proceedings of the 21st VLDB Conference Zurich, Switzerland, 1905 The methods proposed here are general and can be used in conjunctCon with most known symmetric declustering methods.