MAID-Q: Minimizing Tail Latency in Embedded Flash With SMR Disk via -Learning Model

As the mainstream solid-state storage technology, NAND flash has the advantages of tiny size, cost-effective, and high performance, which make it a promising candidate to be embedded into the shingled magnetic recording (SMR) disk to build a faster, denser, and cheaper storage system. However, such an embedded flash with SMR (EF-SMR) disk system suffers from lengthy tail-latency due to “reclamation issues” in both the NAND flash and the SMR disk. Our preliminary observations reveal that tremendous idle time intervals exist in real-world scenarios, and few prior works have focused on addressing the tail-latency issue in the EF-SMR disk. In this article, we propose a novel method termed MAID-Q to fully exploit the idle time intervals to minimize the lengthy tail-latency of the EF-SMR disk based on a lightweight reinforcement learning model (i.e., the $Q$ -learning model). In addition, fine-grained block-level space management and a parallel reclamation strategy are proposed to improve the reclamation efficiency and hide the reclamation overheads. The effectiveness of our proposed design was evaluated with realistic I/O traces, and the results show that the proposed design can remedy the tail-latency by 88.31% and improve the overall performance by 79.03%.