HMB-I/O: Fast Track for Handling Urgent I/Os in Nonvolatile Memory Express Solid-State Drives

Abstract

Differentiated I/O services for applications with their own requirements are very important for user satisfaction. Nonvolatile memory express (NVMe) solid-state drive (SSD) architecture can improve the I/O bandwidth with its numerous submission queues, but the quality of service (QoS) of each I/O request is never guaranteed. In particular, if many I/O requests are pending in the submission queues due to a bursty I/O workload, urgent I/O requests can be delayed, and consequently, the QoS requirements of applications that need fast service cannot be met. This paper presents a scheme that handles urgent I/O requests without delay even if there are many pending I/O requests. Since the pending I/O requests in the submission queues cannot be controlled by the host, the host memory buffer (HMB), which is part of the DRAM of the host that can be accessed from the controller, is used to process urgent I/O requests. Instead of sending urgent I/O requests into the SSDs through legacy I/O paths, the latency is removed by directly inserting them into the HMB. Emulator experiments demonstrated that the proposed scheme could reduce the average and tail latencies by up to 99% and 86%, respectively.