Taking advantage of heterogeneity in disk arrays

Abstract

Disk arrays, or RAIDs, have become the solution to increase the capacity and bandwidth of most storage system, but their usage has some limitations because all the disks in the array have to be equal. Nowadays, assuming a homogeneous set of disks to build an array is becoming a not very realistic assumption in many environments, especially in low-cost clusters of workstations. It is difficult to find a disk with the same characteristics as the ones in the array and replacing or adding new disks breaks the homogeneity. In this paper, we propose two block-distribution algorithms (one for RAID0 and an extension for RAID5) that can be used to build disk arrays from a heterogeneous set of disks. We also show that arrays using this algorithm are able to serve many more disk requests per second than when blocks are distributed assuming that all disks have the lowest common speed, which is the solution currently being used.