E2: Abstracting Solid State Devices for (database) systems

SSDs (Solid State Devices or flash disks) usually simulate a disk drive abstraction with a linear address space,providing simple read and write interfaces to the upper-level systems. While such an abstraction supports the legacy systems designed for the hard disk with little modification, it hinders unleashing the hardware features of SSDs, including copy-on-write updates, the in-disk parallelism and the page mapping. These features are intrinsic, hidden behind the disk drive abstraction. Our empirical study on a standard database benchmark reveals that, given the current disk-based abstraction, database systems lose a series of opportunities for exploiting the hardware capability of the SSD. Motivated by the empirical study, we propose E², a new abstraction with a set of new interfaces abstracting the hardware features of the SSD. The principle behind E² is “expose and exploit”: the abstraction exposes those intrinsic features of the SSD to the upper-layer systems such that they can exploit the hardware features for efficiency and functionality. We examine the E² interfaces in the context of database systems, and find that they open up vast opportunities in the co-design between the SSD and the system.