CMFS: Compressed metadata file system for hybrid storage

Storage CLASS Memory (SCM) is a next generation of solid-state, nonvolatile memory. It combines the benefits of a DRAM, such as high performance and robustness, with the low cost of conventional hard-disk. The biggest difference between SCM and NAND FLASH is that SCM can be accessed in byte-granularity and access speed is much faster. PRAM (Phase Change RAM), FRAM(Ferro-electric RAM), MRAM (Magnetic RAM), RRAM (Resistive RAM), and Solid Electrolyte Freitas et al are all SCM. The advent of SCM may possibly to make big improvement in storage landscape. In this work, we develop a file system - CMFS (compress metadata file system), which is used on SCM and NAND flash hierarchical storage environment. We make two contributions in this work. First, we store in-memory data in the SCM to overcome the drawback of the current log-structured file system that the mount time dramatically increases as the scale of NAND flash increases. Compared to YAFFS, we show that this file system requires only minimal time for mounting. Second, considering the physical characteristics of SCM, its scale is an order of magnitude smaller and the cost is much higher than the current storage device, we just store some part of the in-memory data to reduce the requirement size of the SCM. The capacity of SCM which is required by CMFS is much smaller than the current file system for hybrid storage. Compare with the MiNVFS, the capacity requirement by CMFS is reduced to 14%.