PFFS: a scalable flash memory file system for the hybrid architecture of phase-change RAM and NAND flash

In this paper, we present the scalable and efficient flash file system using the combination of NAND and Phase-change RAM (PRAM). Until now, several flash file systems have been developed considering the physical characteristics of NAND flash. However, previous flash file systems still have a high performance overhead and a scalability problem of the mounting time and the memory usage because, in most case, the metadata is written with several words at a single update even though the writes in NAND flash must be performed in terms of page, which is typically 2 KiB. The proposed flash file system called PFFS uses PRAM to mitigate the limitation of NAND flash. The PRAM is a next generation non-volatile memory and good for dealing with word level read/write of a small size of data. PFFS hence separates the metadata from the regular data in a file system and saves them into PRAM. Consequently, the PFFS manages all the files and directories in the PRAM and outperforms other flash file systems. The experimental results show that the performance of PFFS is 25% better than YAFFS2 for small-file writes while matching YAFFS2 performance for large writes and the mouting time and the memory usage of PFFS are O(1).