SAC: A Co-Design Cache Algorithm for Emerging SMR-based High-Density Disks

To satisfy the huge storage capacity requirements of big data, the emerging high-density disks gradually adopt the Shingled Magnetic Recording (SMR) technique. However, the most serious challenge of SMR disks lies in their weak fine-grained random write performance caused by the write amplification inner SMRs and its extremely unbalanced read and write latencies. Although fast storage devices like Flash-based SSDscan be used to boost SMR disks in SMR-based hybrid storage, the optimization targets of existing cache algorithms (e.g., higher popularity for LRU, lower SMR write amplification ratio for MOST) are NOT the crucial factor for the performance of the SMR-based hybrid storage. In this paper, we propose a new SMR-Aware Co-design cache algorithm called SAC to accelerate the SMR-based hybrid storage. SAC adopts a hardware/software co-design method to fit the characteristics of SMR disks and to optimize the crucial factor, i.e., RMW operations inner SMR disks, effectively. Furthermore, SAC also makes a good balance between some conflicting factors, e.g., the data popularity vs. the SMR write amplification and clean cache space vs. dirty cache space. In our evaluations under real-world traces, SAC achieves a 7.5× performance speedup compared with LRU in the write-only mode, and a 2.9× speedup in the read-write mixed mode.