I need to keep some static web mirrors synced in as close to realtime as possible, but I also want it to be somewhat fail-safe (or at least not obvious to the visitors), so if the file server goes down the mount is automatically switched to the local copy. Is there a fs driver out there that can do that? Simply rsyncing isn't a good choice because of the sheer number of files involved. Failing an fs driver, is there some other solution to this problem?
All the servers in question are linux.