UNIX Filesystems: Evolution, Design, and Implementation

Clustered and Distributed Filesystems

With the advent of computer networks, which appeared in the 1970s and became more widespread in the 1980s, the need to share files between machines became essential. Initially, UNIX tools such as uucp and ftp were used to transfer files from one machine to another. However, disks were still relatively expensive; this resulted in a need to access files across the network without local storage.

The 1980s saw a number of different distributed filesystems make an appearance in the UNIX community, including Sun's Network Filesystem (NFS), AT&T's Remote File Sharing (RFS), and CMU's Andrew File System (AFS) which evolved into the DCE Distributed File Service (DFS). Some of the distributed filesystems faded as quickly as they appeared. By far, NFS has been the most successful, being used on tens of thousands of UNIX and non-UNIX operating systems throughout the world.

Distributed filesystems operate around a client/server model, with one of the machines owning an underlying disk-based filesystem and serving files to clients through some well-defined protocol. The protocol and means of transferring files to the user is transparent, with UNIX file semantics being a key goal.

Clustered filesystems by contrast treat a collection of machines and disks as a single entity and provide a fully coherent view of the filesystem from any of the nodes. To the user, ...