R&D: Space-Grained Cleaning Method to Reduce Long-Tail Latency of DM-SMR Disks

ACM Transactions on Embedded Computing Systems has published an article written by Chin-Hsien Wu, Cheng-Tze Lee, Yi-Ren Tsai, Cheng-Yen Wu, National Taiwan University of Science and Technology, Taipei, Taiwan.

Abstract: “DM-SMR (device-managed shingled magnetic recording) disks allocate a portion of disk space as the persistent cache (PC) to address the issue of overlapping tracks during data updates. When the PC space becomes insufficient, a space cleaning is triggered to reclaim its invalid space. However, the space cleaning is time-consuming and contributes to the long-tail latency of DM-SMR disks. In the article, we will propose a space-grained cleaning method that leverages various idle periods to effectively reduce the long-tail latency of DM-SMR disks. The objective is to perform a proper space-grained cleaning for a suitable space region at an appropriate time period, thereby preventing delays in subsequent I/O requests and reducing the long-tail latency associated with DM-SMR disks. The experimental results demonstrate a substantial reduction in the long-tail latency of DM-SMR disks through the proposed method.“