FC: Built-in Flash-cache with fast cleaning for SMR Storage

Shingled Magnetic Recording (SMR) Disks are adopted as a high-density, non-volatile media which significantly precedes conventional disks in both the storing volume and cost. However, time-consuming read-modify-writes (RMWs) significantly degrade the system performance of SMR disks. Current designs devote a portion of disk spaces as a cache to alleviate the negative effect brought by RMWs, however, when the cache is full, the cleaning process becomes the performance bottleneck of the system. This paper presents a hybrid architecture called Flash-cache (FC) to manage the SMR disks by replacing the cache with built-in NAND flash. The performance without triggering a cleaning process of FC can be comparable to that of NAND flash rather than HDDs. Furthermore, FC is capable of shrinking down the large-scale cleaning process and performing much faster cleaning. Our experimental results show that FC can shorten the overall system average response time by over 73% and improve the cleaning efficiency by approximately 11.1 times.