HIOS: A host interface I/O scheduler for Solid State Disks

Garbage collection (GC) and resource contention on I/O buses (channels) are among the critical bottlenecks in Solid State Disks (SSDs) that cannot be easily hidden. Most existing I/O scheduling algorithms in the host interface logic (HIL) of state-of-the-art SSDs are oblivious to such low-level performance bottlenecks in SSDs. As a result, SSDs may violate quality of service (QoS) requirements by not being able to meet the deadlines of I/O requests. In this paper, we propose a novel host interface I/O scheduler that is both GC-aware and QoS-aware. The proposed scheduler redistributes the GC overheads across non-critical I/O requests and reduces channel resource contention. Our experiments with workloads from various application domains reveal that the proposed scheduler reduces the standard deviation for latency over state-of-the-art I/O schedulers used in the HIL by 52.5%, and the worst-case latency by 86.6%. In addition, for I/O requests with sizes smaller than a superpage, our proposed scheduler avoids channel resource conflicts and reduces latency by 29.2% compared to the state-of-the-art.