Metadata Logging in an NFS Server

Over the last few years, there have been several efforts to use logging to improve performance, reliability, and recovery times of file systems. The two major techniques are metadata logging, where the log records metadata changes and is a supplement to the on-disk file system, and log-structured file systems, whose log is their only on-disk representation. When the file system is mainly or wholly accessed through the Network File System (NFS) protocol, it adds new considerations to the suitability of the logging technique. NFS requires that all operations be updated to stable storage before returning. As a result, file system implementations that were effective for local access may perform poorly on an NFS server. This paper analyzes the issues regarding the use of logging on an NFS server, and describes an implementation of a BSD Fast File System (FFS) with metadata logging that performs effectively for a dedicated NFS server.