A Regional Popularity-Aware Cache Replacement Algorithm to Improve the Performance and Lifetime of SSD-based Disk Cache

Flash-based Solid State Drive (SSD) has limitations in terms of cost and lifetime. It is used as a second-level cache between main memory and traditional HDD-based storage widely. Adopting traditional cache algorithms, which are designed primarily depending on temporal locality and popular blocks, to SSD-based second-level disk cache can cause unnecessary cache replacements, which not only degrade the cache performance but also shorten the lifetime of SSD. To overcome this problem, this paper proposes a performance-effective Regional Popularity-Aware Cache replacement algorithm (RPAC). Instead of a single block, the popularity of a region which is constituted by many adjacent disk blocks is recorded and used to determine replacing a block or not. In this way, the spatial locality of disk access is completely leveraged and sequential I/O blocks are gathered in SSD cache. Furthermore, it reduces the number of unnecessary cache replacement and erasure operation on SSD, prolonging its lifetime. We have implemented RPAC in real system and evaluated it by many workloads. Compared to traditional cache algorithms, it improve I/O throughput by up to 53% and reduce cache replacements of SSD up to 98.5%.