Distributed sparing in disk arrays

The authors propose and examine a technique called distributed sparing, which improves the performance of disk arrays by utilizing otherwise unused spare disks in the system. Performance is not only improved in normal mode but it is also improved in degraded mode when a disk has failed and during rebuild. The authors illustrate four methods by which the distributed sparing approach can be applied to large systems with many arrays. By and large, the analysis shows that distributed sparing is particularly effective in small systems with few drives, but it can also be effective in large systems. Unrelated to the performance benefit, the distributed sparing approach also provides an elegant way of ensuring that the spare drives are operational when they need to be used. Without special background testing of the spare drives, traditional sparing approaches have no guarantee that such drives will be operational when needed.<>