LCR: Load-Aware Cache Replacement Algorithm for Flash-Based SSDs

Abstract

Flash-based SSDs are usually equipped with an onboard cache to further improve system performance by smoothing the gap between the upper-level applications and lower-level flash chips. Since modern SSDs are usually composed of multiple flash chips, and the load of flash chips are significantly different, it is very meaningful to be aware of the chip load condition when designing a cache replacement algorithm. Nevertheless, existing cache replacement algorithms only consider to reduce the cache miss ratio so as to reduce the I/O requests to the underlying flash memory as much as possible, none of them considers the load condition of flash chips. In this paper, we propose a Load- aware Cache Replacement algorithm, called LCR, to improve the performance of flash-based SSDs. The basic idea is to give a higher priority to cache the blocks on overloaded flash chips. We evaluate the performance of our scheme by using a trace- driven simulator with multiple real-world workloads, and results show that compared with the most common algorithm LRU and the state-of-the-art algorithm GCaR, LCR reduces the average response time by as much as 39.2% and 12.3%, respectively.