CBW: Reducing Data Write Back with Circular Bubble Write for DM-SMR Disks

As the demand for storage capacity continues to rise, Shingled Magnetic Recording (SMR) disks promise higher storage density through the overlapping of adjacent tracks. However, the sequential write constraint inherent in SMR could result in increased latency during write operations. To balance performance and cost, a portion of SMR storage is used as a persistent cache (PC), employing a log-structured method to enhance write speed. When the PC is full, a garbage collection (GC) policy migrates valid data to the native data area (NDA), freeing up space. However, inefficient data migration can occur if access frequency is not considered, leading to unnecessary writes. To address this issue, we propose the Circular Bubble Write (CBW) scheme, which divides the PC into four areas (including rookie area, rookie buffer, hot area, and cold area) and adaptively places data based on access frequency. This ensures hot data remains in the PC while only cold data migrates to the NDA. The experiment results showed that the CBW scheme could reduce average response time by up to 84% and unnecessary write-backs by up to 95% in write-intensive workloads.