I see lot of how-to's out there about doing a one time migration from 32 to 64 bit. However, I'm interested in something more gradual. I have a multiserver setup that looks as follows:
  • MTA
    • Antispam
    • Antivirus
    • imapproxy
    • memcached
    • mta
    • snmp
    • stats
    • zmconfigd
  • Mailstore
    • convertd
    • ldap
    • logger
    • mailbox
    • snmp
    • spell
    • stats
    • zmconfigd

Each of these servers is running Ubuntu Server 8.04.4. Obviously it is time to upgrade, but I'd prefer to not do a single night migration, so I'm wondering if anyone has written up directions that would allow me to build myself an Ubuntu 12.04.1 64 bit server, and then install the same version of Zimbra. I should be able to run mailbox on the new server, and use the web UI to migrate my accounts to the new server.

The next steps (and where I am the haziest on how this would be accomplished) would be to migrate the LDAP from the old mailstore to the new mail store, and then retire the old server.

At this point I would have a 32 bit MTA, and a 64 bit LDAP & Mailbox server. The last step would be to build a new MTA that is 64bit, and retire the old MTA.

Has anyone ever done it this way before? Are there directions out there for it?