Block-level replacement scheme considering re-write probability for solid state drives

SSDs use multiple NAND flash memory chips as storage media and deploy large sized RAM inside it in order to maintain the FTL mapping table. The rest portion of the inner RAM can be used as buffer. The buffer absorbs the read/write requests by file systems and thus the resulting write requests to NAND flash memory is determined by the buffer replacement scheme. The block-level LRU replacement schemes, which manages the buffer in NAND block unit, generates a large sized write pattern that is NAND-friendly. However, the existing schemes do not consider the re-write probability of each page. This paper presents a new block-level replacement policy for SSDs. The presented scheme evicts only cold pages that its re-write probability is low considering the re-write probability, which can contribute to improve the buffer hit ratio.