DRACO: A Deduplicating FTL for Tangible Extra Capacity

The rapid random access of SSDs enables efficient searching of redundant data and their deduplication. However, the space earned from deduplication cannot be used as permanent storage because it must be reclaimed when deduplication is cancelled as a result of an update to the deduplicated data. To overcome this limitation, we propose a novel FTL scheme that enables the gained capacity to be used as permanent storage space for the file system layer. The proposed approach determines the safe amount of gained capacity that can be provided to the upper layer based on the compression rate prediction scheme. It then secures the required space by compressing cold data when capacity overflow occurs from cancelled deduplication. Our evaluation with a kernel source repository showed that the file system obtained approximately 79 percent additional capacity by the proposed scheme.