Asynchronous Disk Interleaving: Approximating Access Delays

Disk interleaving, or disk striping, distributes a data block across a group of disks and allows parallel transfer of data. Disk interleaving is achieved by dividing a data block into a number of subblocks and placing each subblock on a separate disk. A subblock can be stored on an interleaved disk at a predetermined location (relative to the adjacent subblocks), or it can be stored at any location on the disk. We consider a system where adjacent subblocks are placed independently of each other, we call it an asynchronous disk interleaving system, and analyze its performance implications. Since each of the disks in such a system is treated independently while being accessed as a group, the access delay of a request for a data block in an n-disk system is the maximum of n access delays. Using approximate analysis, we obtain a simple expression for the expected value of such a maximum delay. The analytic approximation is verified by simulation using trace data, the relative error is found to be at most 6%. © 1991 IEEE