FSTL: A Framework to Design and Explore Shingled Magnetic Recording Translation Layers

We introduce FSTL, a Framework for Shingled Translation Layers: a toolkit for implementing host-side block translation layers for Shingled Magnetic Recording (SMR) drives. It provides a Linux kernel implementation of key translation mechanisms (write allocation, LBA translation, map persistence, and consistent copying) while allowing translation policy (e.g. layout, cleaning algorithms, crash recovery) to be implemented in a user-space controller which communicates through an ioctl-based API to the kernel data plane. Due to its use of a journaled write format, FSTL-based translation layers are able to handle synchronous and durable writes to random LBAs at high speed. We describe the architecture and implementation of FSTL, and present two FSTL-based translation layers implemented in 400 lines of Python each. Despite the simplicity of the controllers, experiments show our first translation layer performing 1.5x to 10x better than a drive-managed translation layer on trace replay experiments, with performance roughly comparable to the drive-managed device for real file system-based benchmarks; the second translation layer, based on a full-volume extent map, is shown to offer significantly better performance than prior work. Furthermore, we implement and evaluate three cleaning algorithms to demonstrate how FSTL-based translation layers may be readily modified, while still offering the robustness needed for long-duration benchmarks and use.