PrePrint: An Efficient Penalty-Aware Cache to Improve the Performance of Parity-Based Disk Arrays under Faulty Conditions

from IEEE Transactions on Parallel and Distributed Systems http://www.computer.org/portal/web/csdl/doi/10.1109/TPDS.2012.266

The buffer cache plays an essential role in smoothing the gap between the upper-level computational components and the lower-level storage devices. A good buffer cache management scheme should be beneficial to not only the computational components, but also the storage components by reducing disk I/Os. Existing cache replacement algorithms are well optimized for disks in normal mode, but inefficient under faulty scenarios, such as a parity-based disk array with faulty disk(s). To address this issue, we propose a novel asymmetric buffer cache replacement strategy, named Victim Disk(s) First (VDF) cache, to improve the reliability and performance of a storage system consisting of a buffer cache and disk arrays. VDF cache gives higher priority to cache the blocks on the faulty disks when the disk array fails, thus reducing the I/Os addressed directly to the faulty disks. To verify the effectiveness of the VDF cache, we have integrated VDF into the popular cache algorithms LFU and LRU, named VDF-LFU and VDF-LRU, respectively. We have conducted intensive simulations as well as a prototype implementation for disk arrays to tolerate one disk failure (RAID-5) and two disk failures (RAID-6). The results show that VDF can effectively reduce disk I/Os to surviving disks, thus speed up the online recovery and/or improve the maximum system service rate.

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