SoftSSD: Software-defined SSD Development Platform for Rapid Flash Firmware Prototyping

Recently, solid-state drives (SSDs) have been used in a wide range of emerging data processing systems. Essentially, an SSD is a complex embedded system that involves both hardware and software design. For the latter, firmware modules such as the flash translation layer (FTL) orchestrate internal operations and flash management, and are crucial to the overall I/O performance of an SSD. Despite the rapid development of new features of SSDs in the market, the research of flash firmware has been mostly simulation-based due to the lack of a realistic and extensible SSD development platform. In this paper, we propose SoftSSD, a software-defined SSD development platform for rapid flash firmware prototyping. The core of SoftSSD is a novel framework with an event-driven programming model. With the programming model, new FTL algorithms can be implemented and integrated into a full-featured flash firmware in a straightforward way. The resulting flash firmware can be deployed and evaluated on a hardware development board, which can be connected to a host system via PCIe and serve as a normal NVMe SSD. Different from existing hardware-oriented development platforms, SoftSSD implements the majority of SSD components (e.g., host interface controller) in software so that data flows and internal states that were once confined in the hardware can now be examined with a software debugger, providing the observability and the extensibility that are critical to the rapid prototyping and research of flash firmware. This paper describes the programming model and hardware design of SoftSSD. We also perform experiments with real application workloads on a prototype board to demonstrate the performance and usefulness of SoftSSD and released the open-source code of SoftSSD for public access.