h-Buffer: An Adaptive Buffer Management Scheme for Flash-Based Storage Devices

Abstract

Due to the limitations of flash memory, such as asymmetric I/O latencies and not-in-place update, there are two kinds of buffer replacement algorithms: page-clustered policy and group-clustered policy. That the former one organizes pages at page-level makes it easy to deal with hot pages, but shows a bad performance when the buffer size is large enough. The latter one organizes pages at group-level, which usually ignores the read request from the host as the RAM size inside SSDs (Solid State Disks) is limited. However, as the read/write latency for flash memory is about 1:10, and most of desk and server application programs are read-intensive, applying a small portion of buffer space for some hot clean pages will benefit most. In this paper, we propose such a buffer management scheme called h-Buffer with three lists. Applying less than 7.125% of the buffer size for clean pages, h-Buffer considers both the write and read requests by the adoption of a replacement policy, a write-back policy and a HL (hot list) compensating policy. Unlike certain existing algorithms, it does not only consider the recency and frequency of page references, but also interacts with the buffer capacities and FTL timely. Experiment results show that the erase count, write count, read count and run time of h-Buffer decrease 50% over traditional algorithms on average.