Supporting Transactional Atomicity in Flash Storage Devices

Flash memory does not allow data to be updated in place, and the copy-on-write strategy is adopted by most flash storage devices. The copy-on-write strategy in modern FTLs provides an excellent opportunity for offloading the burden of guaranteeing the transactional atomicity from a host system to flash storage and for supporting atomic update propagation. This paper presents X-FTL as a model case of exploiting the opportunity in flash storage to achieve the transactional atomicity in a simple and efficient way. X-FTL drastically improves the transactional throughput almost for free without resorting to costly journaling schemes. We have implemented X-FTL on an SSD development board called OpenSSD, and modified SQLite and ext4 file system minimally to make them compatible with the extended abstractions provided by X-FTL. We demonstrate the effectiveness of X-FTL using real and synthetic SQLite workloads for smartphone applications.