FLAP: Flash-aware Prefetching for Improving SSD-based Disk Cache

In modern enterprise storage systems, there is a trend that using NAND flash based solid state disks (SSDs) as a second-level disk cache to reduce the slow access to hard disk drives (HDDs) by caching the hot data of HDDs with SSDs. However, using SSDs for both caching and prefetching has rarely been discussed due to the performance penalty caused by unsuccessful prefetching, including garbage collection cost and disk bandwidth wasting. In this paper, a FLash-Aware Prefetching (FLAP) scheme has been presented to provide aggressive prefetching for improving the performance of sequential disk accesses. FLAP has been evaluated using well known real-world workloads. Experiment results show that FLAP can offer performance improvement under sequential workloads compared with pure caching, while reducing the internal garbage collection of SSDs.