一种针对iSCSI存储的缓存替换算法

摘要

由于IP网络的带宽限制和较长的传输延迟,为了完成数据的请求,iSCSI initiator和iSCSI target在确认对方发出的状态或控制命令前将等待更多的时间.iSCSI协议中通信开销所占的比重较大,因此iSCSI存储的缓存数据载入开销不同于传统的直连存储.现有的替换算法研究主要关注缓存命中率的提高,忽略了通过降低失效数据的载入开销来提高缓存系统性能.提出了一种针对iSCSI存储的缓存替换算法CFL-LRU,该算法不仅考虑访问时间和访问频度,还将考虑缓存页面的逻辑块地址连续度,从而在兼顾命中率的同时降低失效数据的缓存载入开销.实验结果表明,在各种不同的典型负载和缓存大小下,CFL-LRU的效果好于其它替换算法.%Due to the bandwidth restriction and the long delay of IP network,iSCSI initiator and iSCSI target have to wait for a longer time until they acknowledge the status or the control command sent by the other party.The communication of iSCSI protocol takes a large part of the total cost.Therefore,the cache data's loading cost of iSCSI storage is different from the traditional direct attached storage.The existing researches focused on achieving high cache hit ratios,but rarely paid attention to reducing the loading cost of miss data for improving the storage system performance.In the paper,a cache replacement algorithm called CFL-LRU (LRU Combined with Frequency and data Length) was proposed for iSCSI storage.The algorithm not only considers the time and the frequency but also takes into account the logical block address continuity of pages,thereby compromising the hit rate and the miss penalty.Our trace-driven simulation results show that,for different kinds of workloads and cache size,the CFLLRU outperforms the others.