Dynamic File Cache Optimization for Hybrid SSDs with High-Density and Low-Cost Flash Memory

Over the last few years, hybrid solid-state drives (SSDs) have been widely adopted due to their high performance and high capacity. Devices equipped with hybrid SSDs can be utilized to cache files from the network for performance improvement. However, this paper finds an interesting observation, that is, the efficiency of hybrid SSDs is significantly degraded instead of improved when too much data is cached. This is because the internal mode switching between different types of flash memory is affected by the device utilization. This paper proposes a dynamic file cache optimization scheme for hybrid SSDs, DFCache, which optimizes the device's efficiency and limits unreasonable space consumption. DFCache includes two key ideas, dynamic cache space management, and intelligent cache file sifting. DFCache is implemented in Linux kernel and tested under real hybrid SSDs. Experimental results show that the I/O performance outperforms the state-of-the-art by up to 3.7x.