Second chance replacement considering a garbage collection cost of FAST scheme

NAND-based storage devices deploy the flash translation layer (FTL) in order to emulate the block device characteristics because NAND flash memory does not support the overwrite operation. The FTL schemes that use log blocks such as the BAST and the FAST scheme are adequate for the devices with harsh memory. This paper presents the log block replacement scheme to improve the performance of the FAST FTL scheme. The presented scheme considers the number of valid pages of the candidate log block when selecting the victim log block, because the cost of the garbage collection decreases as the number of valid pages in the victim log block is less. The presented scheme gives the second chance to the candidate log block if its valid pages are more than the threshold. The simulation shows that the presented scheme improves the performance of the FAST scheme up to 5.0 %. The improvement is more conspicuous as more NAND blocks are used as log blocks.