Software-defined Fusion Storage System For PCM And NAND Flash

Currently, most SSDs use the FTL algorithm to shield NAND Flash's disadvantages and improve the applicability. However, the SSD wrapped as a black box structure can hardly obtain more semantic information of the host data accessing requests. Hence the FTL could improve system performance by data organizing and scheduling in terms of the semantic information of accessing data. Meanwhile, the file system or I/O scheduling algorithm designed for disks are also not suitable for SSD, and can hardly obtain physical characteristics and statistical information of SSD to do the optimization.In order to meet the application requirements and improve the performance, this paper proposes a software-defined fusion storage system for PCM(Phase Change Memory) and NAND Flash. Fuse non-volatile storage device of better performance, PCM, into SSD, and use it as the same level storage or buffer of NAND Flash according to access pattern of host data. In order to maximize the performance advantages of PCM/NAND Flash, the storage device exposes the channels, erases counts and data distribution of PCM/NAND Flash to the host. And implement the FTL algorithm in host side. The storage system is designed as a hardware/software co-designed fusion storage system. Optimize the interface between host and device, shorten the data accessing I/O path, file systems and application programs can call interface to access PCM and NAND Flash directly, maximize the advantages of the PCM and NAND Flash. In order to achieve the design goals, Host Fusion Storage Layer(HFSL) is designed to support flexible I/O schedule algorithm and allocation size variable address mapping in the persistent high performance and flexibility of storage system. And design dedicated fusion storage system for users to meet the application requirements without changing the hardware. Extensive experimental results demonstrate the efficiency of the proposed schemes.