HasFS: optimizing file system consistency mechanism on NVM-based hybrid storage architecture

In order to protect the data during system crash, traditional DRAM–DISK architecture file systems (e.g., EXT4) need to synchronize the dirty metadata and data from the memory to disk. At the same time, the disk synchronization may break the consistency of file system upon a crash, so traditional file systems use some mechanisms to guarantee the file system consistency when the dirty metadata and data is synchronized onto persistent storage devices (e.g., HDD and SSD). Journaling is a consistency mechanism widely used by file systems. We observe that the overhead of periodic disk synchronization and journaling is high. Emerging non-volatile memories (NVMs) can be potentially utilized to reduce these overheads. In this paper, we present hybrid architecture for storage file system (HasFS), a file system designed for the DRAM–NVM–DISK architecture. HasFS extends the main memory with NVM and considers NVM as a persistent page cache to eliminate the periodic disk synchronization overhead of dirty data. Then we design an efficient consistency mechanism based on the hybrid memory architecture to provide strong (both metadata and data) consistency guarantee with low overhead. The evaluation demonstrates that HasFS outperforms mainstream DRAM–DISK file systems for many workloads. For instance, HasFS has between 1.6X to 46.6X performance improvement over other tested file systems in random write workload. In particular, HasFS outperforms EXT4 without journal in some cases even though HasFS provides metadata and data consistency guarantees (similar to EXT4 with journal data mode).