OCStore: Accelerating Distributed Object Storage with Open-Channel SSDs

SSDs are getting widely used in data centers. It is a critical issue to design efficient software for exploiting the benefits of fast SSD hardware. In this paper, we propose OCStore, an object store based on open-channel SSDs for distributed object storage system. OCStore manages the objects directly on raw flash memory, mitigating redundant functions across the object store, the file system, and the FTL layers. It provides streamed transactional update, which not only ensures the multi-page atomicity leveraging the non-overwrite flash write features, but also provides isolation for independent I/O streams while enabling parallel accesses to different channels. OCStore also coordinates different channels to enable transaction-aware scheduling, so as to reduce transaction-level latency and provide low response time to distributed storage. We implement OCStore in Linux kernel on the real open-channel SSDs, and evaluate them as OSDs in Ceph. Evaluations show that OCStore outperforms state-of-the-art object stores by 1.5× to 3.0×, while providing much lower and stable latencies, and decreases up to 70% write traffic under heavy workloads.