Design and implementation of a journaling file system for phase-change memory

Journaling file systems are widely used in modern computer systems as they provide high reliability at reasonable cost. However, existing journaling file systems are not efficient for emerging PCM (phase-change memory) storage because they are optimized for hard disks. Specifically, the large amount of data that they write during journaling degrades the performance of PCM storage seriously as it has a long write latency. In this paper, we present a new journaling file system for PCM, called Shortcut-JFS, that reduces write traffic to PCM by more than half of existing journaling file systems running on block I/O interfaces. To do this, we devise two novel schemes that can be used under byte-addressable I/O interfaces: 1) differential logging that journals only the modified part of a block and 2) in-place checkpointing that eliminates the overhead of block copying. We implement Shortcut-JFS on Linux 2.6.32 and measure the performance of Shortcut-JFS compared to those of existing journaling and log-structured file systems. The results show that the performance improvement of Shortcut-JFS against Ext4 and LFS is 54 and 96 percent, respectively, on average.