通过缓存压缩提高磁盘性能

Leveraging Compressed Cache to Improve Disk Performance

过去的20年里面,主存与硬盘的性能差距以每年50%的速度飞速扩大.造成这种局面的主要原因是磁盘机械器件延迟导致的其性能提升缓慢(每年8%的性能提升).磁盘内部缓存管理对于磁盘的性能有着重要的影响,因为它起到平衡快总线与慢机械器件的中间栋梁作用.缓存介质一般为SRAM,成本昂贵并且容量低.因此,磁盘生产商不会给磁盘装备大容量的缓存.本文提出了一个新的思路来改善这个问题,通过压缩磁盘缓存,提高缓存有效容量以预取更多的数据.为了降低压缩所带来的复杂度与负作用,我们只压缩读请求服务后预取的数据.通过Disksim模拟实现,并测试合成负载,我们得到了较好的结果.实验证明,随着压缩率的改善,磁盘平均响应时间最大减少43.5%,命中率最高提高到3倍.

Over the last two decades,the performance gap between RAM and disk drives has been widened by about 50% per year. This is because the disk access time was improved only about 8% per year due to the mechanical delays. The management of on-board disk cache plays an important role on disk performance, because it can bridge the gap between the high-speed I/O bus and slow mag- netic media. The physical media of on-board disk cache is normally made of SRAM. However,it is very expensive and has low capacity. Therefore, the manufactures normally do not equip disk drives with big size on-board disk cache. This paper proposes a new ap- proach to alleviate this issue by compressing the on-board disk cache. To minimize the complexity and side effect of compression, we only compress the sectors fetched by read-ahead. The compression is processed in background without affecting ongoing requests. The scheme is implemented and integrated into DiskSim. Synthetic traces are employed to evaluate the proposed method. Experimental resuits demonstrate that the average response time can be reduced up to 43.5 % with the improvement of the compression ratio, and the hit ratio gets up to 3x improvement.