Many distributed file systems have been designed and deployed, operating on the fast local area networks available to connect machines within a single site. These systems include DOMAIN [9], DS [15], RFS [16], and Sprite [10]. Perhaps the most widespread of distributed file systems to date is a product from Sun Microsystems, NFS [13] [14], extending the popular unix file system so that it operates over local networks. @section sec2-3 Section 2.3: Wide-Area Distributed File Systems