I need to move my system to a new SAN with more storage immediately. Unfortunately, doing repeated, consecutive rsyncs is still taking 5-6 hours on each pass and it's going to be a challenge to find that kind of downtime window.

I'm wondering how practical it is to setup the proxy, add a second server to the mix, migrate the mailboxes with the system up, and then remove the old server and the proxy.

I'm sure the docs are out there for the first half of the equation, but scaling back down is what I'm afraid of having trouble with. Is this a plausible way of doing things or do I just need to bite the bullet and insist on some downtime?