Creating redundant content under Linux is a field that is still in a state of flux. The most mature technology for providing distributed access to files is NFS. Performance issues relating to the current NFS implementation have lead to various projects including a caching client that works with current release kernels. This unfortunately is not at this time well supported though it is reported to be stable. The main stream NFS implementation for has also undergone a major reworking and the fruits of this are, at the time of writing available in development kernels. Once this implementation comes into main-stream use, NFS under Linux for distributed operations will become more attractive.
Replication of files can be achieved asynchronously using a tool such as rsync. This can be used in conjunction with an access mechanism such as NFS or on servers that house their own content. This type of solution does however suffer from scalability problems and the asynchronous nature of this makes it inappropriate for many applications. Particularly the usefulness of this for serving workstations is extremely limited.
Coda is a solution that provides both access and replication mechanisms. The use of broadcast RPC for writes and a read from one host scheme makes this a more scalable solution. Coda is however still under development and I would not recommend this in a production environment.
The provisioning of redundant content under Linux is area where many gains still need to be made before a satisfactory solution gains wide spread acceptance. At the moment Coda looks like a strong candidate for this although ad hoc solutions based on systems such as NFS and Rsync will have their place for some time to come.