This paper presents the design and implementation of a Highly Available Network File Server (HA-NFS). The paper separates the problem of network file server reliability into three different sub-problems: server reliability, disk reliability, and network reliability. HA-NFS offers a different solution for each: dual-ported disks and impersonation are used to provide server reliability, disk mirroring can be used to provide disk reliability, and optional network replication can be used to provide network reliability.
The implementation shows that HA-NFS provides high availability without the excessive resource overhead or the performance degradation that characterize traditional replication methods. Ongoing operations are not aborted during fail-over and recovery is completely transparent to applications. HA-NFS adheres to the NFS protocol standard and can be used by existing NFS clients without modification. Topics covered within the paper include: