Accelerating File System Metadata Access with Byte-Addressable Nonvolatile Memory

File system performance is dominated by small and frequent metadata access. Metadata is stored as blocks on the hard disk drive. Partial metadata update results in whole-block read or write, which significantly amplifies disk I/O. Furthermore, a huge performance gap between the CPU and disk aggravates this problem. In this article, a file system metadata accelerator (referred to as FSMAC) is proposed to optimize metadata access by efficiently exploiting the persistency and byte-addressability of Nonvolatile Memory (NVM). The FSMAC decouples data and metadata access path, putting data on disk and metadata in byte-addressable NVM at runtime. Thus, data is accessed in a block from I/O the bus and metadata is accessed in a byte-addressable manner from the memory bus. Metadata access is significantly accelerated and metadata I/O is eliminated because metadata in NVM is no longer flushed back to the disk periodically. A lightweight consistency mechanism combining fine-grained versioning and transaction is introduced in the FSMAC. The FSMAC is implemented on a real NVDIMM platform and intensively evaluated under different workloads. Evaluation results show that the FSMAC accelerates the file system up to 49.2 times for synchronized I/O and 7.22 times for asynchronized I/O. Moreover, it can achieve significant performance speedup in network storage and database environment, especially for metadata-intensive or write-dominated workloads.