A New Exploration to Build Flash-Based Storage Systems by Co-designing File System and FTL

Nowadays, data storage and management has become an increasingly significant issue in the world of big data. With its density increasing and price declining, NAND flash has become a ubiquitous storage media in both enterprise and academic community. Flash chips are usually encapsulated into Solid State Drives (SSDs) by the Flash Translation Layer (FTL). SSDs exhibit the same interface as hard disk does thus are applicable to traditional file systems. A large number of technologies have been developed to improve the performance of SSD and SSD-oriented file systems. However, most prior works focused on either FTL or file system, but failed to combine them together. We argue that, it will gain more benefits if file system and FTL cooperate with each other. Contributions of our work include the following aspects. First, we introduce a new method to exploit flash memory by co-designing file system and FTL. Second, we implement out-of-place update at page granularity in file system by changing logical address allocation module to reduce the size of mapping table in FTL. Third, we provide file system with channel allocation by changing FTL and introduce three channel allocation schemes to improve SSDs performance. The evaluation results show that our co-design method gains similar performance as page mapping scheme with small mapping table. With more information to guide channel allocation, the average request response time is reduced by about 20% and throughput is improved by about 24% compared with traditional round-robin scheme. The metadata management in file system and data transmission overhead is negligible.