FC: Built-in flash cache with fast cleaning for SMR storage systems

Abstract

Shingled Magnetic Recording (SMR) disks are adopted as a high-density, non-volatile storage 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 FC (Flash Cache) to manage the SMR disks by replacing the cache with a built-in NAND flash. The performance without triggering a cleaning process of FC can be comparable to that of the NAND flash rather than Hard Disk Drives (HDDs). Furthermore, FC is capable of shortening the large-scale cleaning process and performing much faster cleaning. Our experimental results show that FC can improve both system response time and cleaning efficiency.