A Case for Application-Managed Flash

We propose a new I/O architecture for NAND flash-based SSDs, called application-managed flash (AMF) and present two case studies to show its usefulness. In a typical SSD controller, an intermediate software layer, called the flash translation layer (FTL), is employed between NAND flash chips and a host interface. The main responsibility of an FTL is to provide interoperability with conventional HDDs, but this interoperability comes at the cost of extra hardware resources and degraded I/O performance. The proposed AMF refactors the flash storage architecture so that an SSD controller exposes append-only segments, which do not permit overwriting. This refactoring dramatically improves performance of applications and reduces hardware costs by allowing applications to directly manage flash storage with minimal supports from the SSD controller. In order to understand the benefits of AMF, we study two popular applications: A log-structured file system (F2FS) and a key-value store (RocksDB). Our experiments show that the DRAM in the flash controller is reduced by 128X and the performances of the file system and the key-value store improve by 80 and 54 percent, respectively, over conventional SSDs.