SFS: A Universal File System Cache for Disconnected FS Operations

Abstract

This paper describes the Shadow File System (SFS), a universal file system cache manager on OS/2 and Windows that supports operations involving disconnectable file systems such as network (LAN) file servers, peer-to-peer file servers and docking station disk drives. SFS is a file system redirector that intercepts file system calls to remote file systems. It provides whole-file caching while connected, and uses cached copies to simulate remote file system service during periods of disconnection. Modified files and directories are synchronized at reconnection time; any conflicting updates are reported to the user. We call SFS a universal file system because it is server-independent. This is a result of two features of the design. First, SFS is a client-side-only solution; no changes are required to server code. Second, remote drives are always accessed through drive letters: any remote file system that exports a drive to the local PC operating system can be managed by SFS. SFS is inspired by Coda [Satyanarayanan92, Honeyman93]. a disconnection-enabled caching file system. SFS, however, must deal with issues of consistency, synchronization, and conflict resolution in a multi-server, multi-platform PC computing environment.