Improving Disk Array Reliability Through Expedited Scrubbing

Disk scrubbing periodically scans the contents of a disk array to detect the presence of irrecoverable read errors and reconstitute the contents of the lost blocks using the built-in redundancy of the disk array. We address the issue of scheduling scrubbing runs in disk arrays that can tolerate two disk failures without incurring a data loss, and propose to start an urgent scrubbing run of the whole array whenever a disk failure is detected. Used alone or in combination with periodic scrubbing runs, these expedited runs can improve the mean time to data loss of disk arrays over a wide range of disk repair times. As a result, our technique eliminates the need for frequent scrubbing runs and the need to maintain spare disks and personnel on site to replace failed disks within a twenty-four hour interval.