Metadata Logging in an NFS Server

Uresh Vahalia, EMC Corporation
Cary G. Gray, Abilene Christian University
Dennis Ting, EMC Corporation


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.

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