SIndex: An SSD-based Large-scale Indexing with Deterministic Latency for Cloud Block Storage

The Solid State Drives (SSD) based key-value stores face significant challenges in achieving deterministic access latency. We experimentally observe the long-tail latency is mainly caused by I/O blocking induced by SSD's internal tasks. In this paper, we propose an SSD-based SIndex to store hundreds of billions of block-mapping entries for the latency-critical cloud block storage. To hide the latency fluctuations induced by garbage collection and buffer flushing, SIndex proposes an inter-SSD I/O scheduling based on read/write separation and SSD state transition, while adopting opportunistic request speculation and balancing mechanism to mitigate read disturbance and I/O contention. Moreover, SIndex introduces a write-staging buffer cache and a two-stage sync mechanism to preferentially buffer updated data before synchronizing them to SSDs. We evaluate the SIndex prototype with a variety of benchmarks and real-world traces on commodity SSDs. SIndex is demonstrated to outperform RocksDB and other approaches by up to 11.2 × in tail latency without affecting the throughput performance.