> re: mail servers specifically, there are two seperate classes of storage > that would need replication... One is the mail spools and queues as > used by the MTA (postfix, sendmail, etc), and the other are the user > mail folder(s) as used by the local delivery agent (procmail or > whattever), and read by the mail client (pop, imap). No, mail spools/queues do not need replication. Stuff in the queue are usually deleted in a second and such dynamic change is not worth replicating. If you do put the queue on a distributed filesystem, in most cases you cannot have more than one instance running save for sendmail. The only thing that the MTA needs is the user information database and that is what needs replicating both for the MTA and the pop/imap server software, not the queues. Then the mail store, including configuration files for the local delivery agent in use, needs replication.