HLRU: Hybrid buffer replacement scheme for Solid State Drives

This paper presents buffer replacement schemes for Solid State Drives (SSDs). SSDs consist of multiple NAND flash memory chips, and deploy internal RAM or NVRAM to maintain the mapping table of flash translation layer. The available internal RAM can be used as buffer to absorb a portion of the read/write requests. In order to maximize the effect of the buffer, we have to increase the buffer hit ratio with generating NAND-friendly access pattern. The presented buffer replacement schemes prioritize hot pages that are likely to be re-written in order to increase the buffer hit ratio. In order to generate NAND-friendly write pattern, the presented scheme perform a replacement in a NAND block unit, because NAND-based storage delivers a good performance when the average write request is large in size. The trace-drive simulation shows that the presented schemes deliver a good performance.