I am doing something like this for a number of installation using the rsync contrib from Dungog.net. Two identical servers used as file server, all ibays from the online server are replicated using rsync (over ssh) onto a standby server. Rsync jobs can be scheduled at regular intervals, i.e. every hours or whatever. In our particular case, we rsync evey four hours, this allows the retrieval of files deleted by accident on the main server.