Victim disk first: an asymmetric cache to boost the performance of disk arrays under faulty conditions
Shenggang Wan, Qiang Cao, Jianzhong Huang, Siyi Li, Xin Li, Shenghui Zhan, Li Hong Yu, Changsheng M. Xie, Xubin He · 2011
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 to 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 (or faulty) Disk(s) First (VDF) cache, to improve the reliability and performance of a storage system consisting of a buffer cache and disk arrays. The basic idea is to give higher priority to cache the blocks on the faulty disks when the disk array fails, thus reducing the I/Os directed to the faulty disks. To verify the effectiveness of the VDF cache, we have integrated VDF into two popular cache algorithms LFU and LRU, named VDF-LFU and VDF-LRU, respectively. We have conducted extensive simulations as well as a prototype implementation. The simulation results show that VDF-LFU can reduce disk I/Os to surviving disks by up to 42.3 % and VDF-LRU can reduce those by up to 36.2%. Our measurement results also show that VDF-LFU can speed up the online recovery by up to 46.3 % under a spare-rebuilding mode with online reconstruction, or improve the maximum system service rate by up to 47.7 % under a degraded mode without a reconstruction workload. Similarly, VDF-LRU can speed up the online recovery by up to 34.6%, or improve the system service rate by up to 28.4%. 1