A large body of research work on flash-based SSDs has been conducted in the recent years. Most work uses simulation as an evaluation method. Simulation is easy to use but lacks real system interaction and cannot be used to run real workloads or applications directly.

FlashEm is a real-time flash-based SSD emulator. We expose the emulated device to the system as a block device, so it can run real workloads and applications. We used several techniques to reduce the computational overhead of FlashEm. Our evaluation results show that it is accurate to use FlashEm to evaluate important metrics with common types of flash-based SSDs.

Due to the closed nature of commercial devices, most research on SSDs is performed using simulation or emulation. Without implementation in real devices, it can be difficult to judge the true benefit of the proposed designs. With hardware prototyping, we can evaluate both the difficulty in implementing new designs and the performance of such designs. We built a hardware prototype of the Nameless Write SSD using the OpenSSD Jasmine board. While the flash-translation layer changes were straightforward, we discovered unexpected complexities in implementing extensions to the storage interface.

The File System De-Virtualizer (FSDV) is a system to dynamically remove a layer of indirection common in modern storage stacks, thus decreasing the indirection space and performance costs. FSDV is a light-weight and flexible tool that de-virtualizes data by changing file system pointers to use device physical addresses. When FSDV is not running, the file system and the device both maintain their virtualization layers and perform normal I/O operations. We implemented FSDV with the ext3 file system and an emulated flash-based SSDs.

Our evaluation results show that FSDV can dynamically reduce indirection mapping table space while preserving the foreground I/O performance. We also demonstrate that with our design of FSDV, the changes needed in file system, flash devices, and device interface are small.

FlashTier is a system architecture built upon solid-state cache (SSC), a flash device with an interface designed for caching. The FlashTier design addresses three limitations of using traditional SSDs for caching. First, FlashTier provides a unified logical address space to reduce the cost of cache block management within both the OS and the SSD. Second, FlashTier provides cache consistency guarantees allowing the cached data to be used following a crash. Finally, FlashTier leverages cache behavior to silently evict data blocks during garbage collection to improve performance of the SSC.

Primary storage systems contain only moderate degree of duplication and do not benefit greatly from deduplication. Instead of removing duplicates, we propose a duplication aware disk array (DADA), which recognizes and keeps duplicate contents on disks and make use of its knowledge of duplicates to improve the reliability and availability of disk arrays in various ways. First, DADA can be used to reduce the time spent on disk scrubbing to detect latent sector errors (LSE). Second, DADA reduces RAID reconstruction time during recovery. Finally, DADA provide better reliability than a default RAID array using its knowledge of data duplication.