CSR: Small: Host-Assisted, Software-Defined Solid-State Disk

在过去的二十年里，基于闪存的存储已经从一种相对不为人所知的小众存储技术悄悄发展到移动和嵌入式介质的选择，并以固态硬盘(SSD)的形式在笔记本电脑和服务器领域取得了重大进展。越来越多的应用程序使用固态硬盘，趋势表明固态硬盘使用量将显著增长。然而，固态硬盘不是灵丹妙药-事实上，所有商用固态硬盘中的闪存固件都非常僵硬，对输入/输出(I/O)工作负载的适应性极差，这带来了严峻的挑战，包括每个固态硬盘的固件成本增加、固件缺乏灵活性以及辅助固态硬盘硬件限制。这项工作将解决这些关键问题。该研究将调查固态硬盘应如何通过软件定义实现其在各种I/O工作负载下实现最佳性能所需的灵活性。这将管理每个SSD的僵化固件副本的重复成本，并将当前固件推向更通用和更具延展性的软件空间。另一个探索领域将是调查如何使SSD能够与主机协作，以便两端的资源可以共享到更灵活和更高性能的I/O设备。这将防止板载固态硬盘辅助硬件过度/未充分利用，使主机能够利用固态硬盘本身的特定于工作负载的优化，而不是将数据推送回主机。提高了驱动基于闪存的固态硬盘的机制的灵活性，使系统管理员能够针对使用中的工作负载调整闪存。增加主机和闪存设备之间的合作和透明度应该能够改进应用程序/库/设备级别的优化，这在当前僵化和协议混淆的制度下是不可能的。在主机和固态硬盘之间智能共享辅助硬件(主要是计算和内存)，将允许在主机的计算和内存能力的情况下执行更昂贵的固态硬盘优化，并在固态硬盘对底层数据的局部性情况下执行更智能的I/O优化。此外，将SSD相关任务带到主机侧可以实现应用线程和I/O线程的共同优化，从而潜在地改进计算、通信和I/O，并且类似地，SSD任务可以与SSD侧上的应用线程共同优化，从而导致更高效的活动闪存系统。

Over the past two decades flash-based storage has crept up from a niche and relatively unknown storage technology to the mobile and embedded medium of choice, and made significant in-roads in the laptop and server arenas in the incarnation of Solid State Disk (SSD). Increasingly, many applications use SSDs and trends indicate that SSD usage will grow significantly. However, SSDs are no silver bullet - in reality, the flash firmware in all commercial SSDs is very rigid and highly unadaptable across input/output (I/O) workloads creating sincere challenges which include the added cost of firmware per SSD, firmware inflexibility, and assisting SSD hardware limitations. This work will address these key issues. The research will investigate how SSDs should achieve the flexibility they need to perform best for a variety of I/O workloads by being software-defined. This manages the repeating cost of a copy of inflexible firmware for each SSD, and will push the current firmware into the more general and malleable software space. Another area of exploration will be to investigate how SSDs could be made capable of collaborating with the host such that resources on both sides can be shared towards a more flexible and higher-performing I/O device. This will prevent on-board SSD assisting hardware from being vastly over/under utilized, enabling the host to take advantage of workload-specific optimizations on the SSD itself instead of pushing the data back to the host. Increased flexibility in the mechanisms that drive flash-based SSDs will provide system administrators the ability to tune their flash storage for workloads in use. Increased cooperation and transparency between the host and the flash device should enable improved application/library/device-level optimizations that are impossible under the current rigid and protocol-obfuscated regime. Intelligent sharing of assisting hardware (mainly compute and memory) across the host and SSD will enable more expensive SSD optimizations to be performed given the host's compute and memory power, and more clever I/O optimizations to be performed given the SSD's locality to the underlying data. Further, bringing SSD related tasks to the host side can enable co-optimization of application threads and I/O threads, improving potentially computation, communication, and I/O, and similarly, SSD tasks can be co-optimized with application threads on the SSD side, leading to a more efficient active flash system.