SFCM: A SSD-Friendly Cache Management Policy for Hybrid Storage Systems

Abstract

With the growing popularity of flash memory, solid state drivers (SSD) based on flash memory have been widely used in various kinds of applications. Compared with conventional magnetic disk, SSD can provide higher access bandwidth and lower access latency. However, it will not completely replace the disk as the secondary storage in the short run due to its inherent properties such as asymmetric read/write, high price of per gigabyte etc. Integrating SSD and magnetic disk together can make full use of different performance advantages, so as to obtain good high performance and low cost. This paper proposes SSD-friendly cache management scheme (SFCM) that use SSD as a cache layer between main memory and magnetic disk. For the pages evicted by buffer manager, SFCM conditionally caches them in SSD according to the state of the page and the different replacement cost. Due to the quick access performance of SSD, SFCM can improve the performance of cache management when the destination page resides in SSD. In view of the poor random write performance for SSD, SFCM adopts flash-aware algorithms and data structures to manage the data stored in SSD, which takes care of write patterns and request types’ impacts on system performance. Furthermore, the study proposes a flash-friendly buffer replacement policy which considers the asymmetric I/O cost and the workload access features. We implement the scheme on the multi-level cache storage system based on a simulation platform and evaluate the performance. The experimental results show that SFCM can significantly reduce system response time and disk I/O cost. Adding a flash-based SSD as cache extension can make up the performance gap between memory and disk.