GFTL: Group-Level Mapping in Flash Translation Layer to Provide Efficient Address Translation for NAND Flash-Based SSDs

摘要

NAND flash memory has been widely used as data storage devices in consumer electronics, such as tablet computers and smart phones. Logical-to-physical address translation is important for improving the performance of NAND flash-based SSDs. Even though keeping the mapping table in a DRAM can boost the address translation, it is already infeasible to do this as the capacity of SSDs keeps increasing and only a limited part of DRAM will be used as the mapping cache. Orthogonal to the demand-based page-level FTLs, we develop a novel group-level mapping which divides the whole SSD into multiple equal-size groups. To map a logical-page-number to a physical-page-number, it will be translated into a group number and an offset. The group number can be obtained via calculation, and the offset will be retrieved from a recorded mapping entry which can correspond to any position within a group. Group-level mapping reduces the size of mapping table while obtaining the similar flexibility as the page-level mapping. We also design an effective group-level FTL (GFTL) with a block pool management approach. Our simulations show that GFTL improves the hit ratio of mapping cache and thus reduces the average response time.