Coldmap: Extending SSD Lifetime Exploiting Multi-Page Mapping Information

Solid-state drives (SSDs) include flash translation layer (FTL) functions to manage the inherent characteristics of NAND flash memory. One critical aspect of the flash management functions is garbage collection which reclaims NAND flash blocks that include many invalid pages provoked by page data updates. The garbage collection function can degrade the performance and lifespan of an SSD since the garbage collection creates redundant page reads/writes and block erases in an SSD. In order to tackle the performance and cost issues of garbage collection, we propose Coldmap, an efficient garbage collection mechanism based on the multi-page mapping information for duplicated flash pages. We reveal that the duplicated pages mapped by multiple logical pages exhibit a longer lifespan compared to the non-duplicated pages. Coldmap groups the duplicated pages into new flash blocks while garbage collection is performed. Since the duplicated pages grouped in the cold zone blocks exhibit a longer lifetime, the corresponding blocks are erased less frequently, thus Coldmap can minimize the block erase counts. Our evaluation results using FEMU exhibit that Coldmap can effectively improve the performance and lifetime of an SSD by 15.4% and 84.3%, respectively, compared to the existing remapping-based SSD firmware.