This paper describes the design of a network file service that is tolerant to fail-stop failures and can be run on top of a standard network file service. The fault-tolerance is completely transparent, so the resulting file system can support the same set of heterogeneous workstations and applications as the chosen standard supports. To demonstrate that our design can provide the benefit of highly available files at a reasonable cost to the user, we implemented a prototype based on the Sun NFS protocol. Our approach is not limited to being used with NFS, however. The methodology we used should apply to any network file service built along the client-server model.