LSP: A Locality-Aware Strip Prefetching Scheme for Striped Disk Array Systems with Concurrent Accesses

Abstract

In striped disk array systems, the independency of disks for prefetching is more important than parallelism under high concurrency of accesses, based on which strip prefetching with low read cost has more ability to improve the performance of RAID. However, it indiscriminately fetching all the involved strips limits its applicability. To solve this problem, we propose a Locality-aware Strip Prefetching Scheme (LSP), where it keeps track of the users’ accesses and identifies the hot data areas. Only those strips located in the hot data areas will be prefetched and each prefetching request fetches one strip. LSP has several advantages. First, LSP adapts to the evolving workloads in an online and self-tuning fashion and satisfies the striped disk array systems due to the low read cost in each prefetching request. Second, LSP fully exploits the spatial locality in users’ accesses. Here, the spatial locality is more general, which includes multiple simple patterns, such as loop references, sequentiality, reverse references, and other locality-awarded patterns. Third, LSP discriminates the hot data areas from the cold data areas when prefetching, which significantly alleviates the waste of disk bandwidth, optimizes the cache utilization and improves the prefetching accuracy. We have implemented the prototype of LSP algorithm in Linux kernel 2.6.18. The experimental results show that LSP outperforms SP and Sequential prefetching (SEQP) by up to 22.4% and 24.1% in terms of the average response time, and by up to 1.5 times and 2.3 times in terms of throughput, respectively.