Reptail: Cutting Storage Tail Latency with Inherent Redundancy

Mission-critical edge applications require both low latency and strict data safety. Although emerging ultra-dense SSDs can extend the amount of data edge servers can process, the reduced parallelism can worsen read tail latency and violate deadlines. To cut ultra-dense SSDs’ read tail latency, we propose Reptail, a co-design of host OS and SSD, that exploits the inherent redundancy in transactional systems. We use journaling file system to show how exposing SSD to host OS’s redundancy semantics can improve its read scheduling. We evaluate Reptail with diverse workloads and find more than 20% latency improvements in the 95th and 99th percentile.