montage: NVM-based scalable synchronization framework for crash-consistent file systems

In file systems, a single write system call can make multiple modifications to data and metadata, but such changes are not flushed in an atomic way. To retain the consistency of file systems, conventional approaches guarantee crash consistency in exchange for sacrificing system performance. To mitigate the performance penalty, non-volatile memory (NVM) technologies are believed to be a good candidate for this purpose owing to their low latency and byte-addressibility. However, none of the prior proposals that exploit NVM provide both scalability and strict ordering of modifications. In this article, we propose montage, a crash consistency framework for file systems that consists of two parts. First, montage splits NVM space into multiple staging areas and synchronizes the flushing of modifications these to the storage device. Second, montage uses the pipelined architecture to speed up data flushing to storage. We apply montage to two journaling file systems (ext4 and JFS) and evaluate them on a multicore server with high-performance storage. The evaluation results demonstrate that our design exhibits better performance by a wide margin than recent NVM-based journaling file systems.