Design And Implementation Of A PCM File System

As an emerging nonvolatile memory, PCM(Phase Change Memory)exhibits someremarkable features, such as fast access, nonvolatile and Byte-addressable. PCM uses theresistance difference between amorphous and crystal state to record bit information, Itsread and write performance is the same order of magnitude with DRAM. Traditional filesystems are established in the standard block device such as disk, and can’t exploit PCMcharacteristics. There is not only a waste of space, but also the loss of PCM performance iftraditional file systems are directly employed. The design of new file system for PCM hasbecome a hot research area.This paper presents a special file system designed for PCM, PCMFSwhich fully takesinto account the low access delay and costper bit of PCM, and improves storage efficiency.PCMFS totally supports the VFS(virtual file system) framework and directly build thedata structure such as inode. Metadata structures and relevant operations also be simplifiedto reduce corresponding latency. PCMFS integrates inode table and the data area that areassigned by both sides to the middle, so that it is adaptable for the requirements ofdifferent application scenarios for the number of inode and data block. PCMFS alsodesigns the DIT(deleted inode table) to deal with the deleted inode which can reduce datahole.Besides, in order to ensure space utilization at any time and under any workload,PCMFS also introduces a mechanism for data migration. Finally, the PCMFS prototype isimplemented in Linux platform.We evaluate PCMFS against ext2on ramdisk, ramfs, and tmpfs. The result showsthat PMCFS is12%higher than ext2on ramdisk on space utilization,23.3%higher thanext2on ramdisk and4.5%lower than ramfs and tmpfs on average in access latency.Considering the ramfs and tmpfs are specific file systems for DRAM, the performance ofPCMFS is excellent enough. Besides, PCMFS has an advantage in space saving.