CSR: Medium: Rethinking Distributed SSD Storage Systems

现代存储技术，如固态磁盘（ssd），通过增加密度来增加容量：在相同的物理介质中表示更多的数字位。为了做到这一点，它们表示数据的误差范围缩小了，结果误码率上升了。虽然磁盘使用纠错码来掩盖此类位错误，但由于磁盘块被（过度）写入，误码率会随着磁盘块的老化而上升，最终磁盘出现故障。因此，随着密度的增加，磁盘的预期寿命下降了。本研究通过对存储栈的跨层设计来重新思考如何构建可扩展且经济高效的存储。对于大多数数据中心应用程序，对象已经在多个设备之间进行了复制，可以利用这种应用程序层冗余来提高可靠性。因此，本研究探索了一种SSD存储系统端到端可靠性的新方法：数据中心闪存设备应该远不那么可靠，并将错误可见性和纠正推到分布式应用层。提供这种整体的跨层方法的设计挑战和含义通过三个研究重点进行了探讨：在单个磁盘层、在本地文件系统和在分布式存储系统层。通过将磁盘的生命周期延长几个数量级，这项研究有可能采用新的SSD存储技术，显著节省成本，并使新的应用程序能够使用SSD。由于新一代SSD技术的生命周期缩短，大型数据中心应用程序无法在许多场景中集成这些新一代技术（例如，写速率高的工作负载，包括数据库和缓存）。考虑到这项研究在可靠性改进方面的潜力，它提供了一条走出硬件可靠性悬崖的潜在途径。与这项研究相关的代码、数据和结果将通过一个git存储库提供，该存储库公开托管在https://github.com/princeton-sns/crosslayer-storage/上。材料将在整个奖项期限内以及至少五年后提供。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Modern storage technologies, such as solid-state disks (SSDs), have increased their capacity by increasing density: representing more digital bits in the same physical media. To do so, their margin of error for representing data has shrunk, and the resulting bit error rate has risen. While disks employ error correcting codes to mask such bit errors, these error rates rise as disk blocks age, by being (over)written, and eventually the disk fails. Thus, as density has risen, disks' expected lifetimes have plunged. This research rethinks how to build scalable and cost-effective storage through a cross-layer design to the storage stack.For most datacenter applications, objects are already replicated between multiple devices, and this application-layer redundancy can be leveraged for increased reliability. This research thus explores a new approach for end-to-end reliability for SSD storage systems: datacenter flash devices should be far less reliable and push error visibility and correction up to the distributed application layer. The design challenges and implications of providing such a holistic, cross-layer approach are explored through three research thrusts: at the individual disk layer, at the local file system, and at the distributed storage system layer.By extending the lifecycle of disks by several orders of magnitude, this research has the potential for the adoption of new SSD storage technologies, significant cost savings, and enabling new applications to use SSDs. Due to the plunging lifecycles of newer generations of SSD technologies, large datacenter applications have been unable to integrate these new generations in a number of scenarios (e.g., workloads with heavy write rates, including databases and caches). Given this research's potential for orders of magnitude of reliability improvements, it provides a potential path out from this reliability cliff of the hardware.Code, data, and results relating to this research will be made available via a git repository, hosted publicly at https://github.com/princeton-sns/crosslayer-storage/. Materials will be available throughout the Award term and at least five years following it.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.