HBM: A hybrid buffer management scheme for solid state disks

Abstract

Random writes significantly limit the application of flash memory in enterprise environment due to its poor latency and high garbage collection overhead. Several buffer management schemes for flash memory have been proposed to overcome this issue, which operate either at page or block granularity. Traditional page-based buffer management schemes leverage temporal locality to pursue buffer hit ratio improvement without considering sequentiality of flushed data. Current block-based buffer management schemes exploit spatial locality to improve sequentiality of write accesses passed to flash memory at a cost of low buffer utilization. None of them achieves both high buffer hit ratio and good sequentiality at the same time, which are two critical factors determining the efficiency of buffer management for flash memory. In this thesis, we propose a novel hybrid buffer management scheme referred to as HBM, which divides buffer space into page region and block region to make full use of both temporal and spatial localities among accesses in hybrid form. HBM dynamically balances our two objectives of high buffer hit ratio and good sequentiality for different workloads. HBM can make more sequential accesses passed to flash memory and efficiently improve the performance. We have extensively evaluated HBM under various enterprise workloads. Our benchmark results conclusively demonstrate that HBM can achieve up to 84% performance improvement and 85% garbage collection overhead reduction compared to existing buffer management schemes. Meanwhile, the energy consumption of flash chips for HBM is limited.