I stumbled across this wiki article and am thinking this is a good idea:

Server Live sync - Zimbra :: Wiki

I just upgraded to version 8 with Ubuntu 12.04 LTS. It is a physical server and I decided to spin up a VM with similar specs and try to follow the wiki. I do have few questions on how I might go about this. I plan to put this server on the same subnet. Should I different hostname or use the same hostname? Does that even matter? I am using a Comodo SSL cert that I would like to apply to this server as well if at all possible that is really the reason I am concerned with the hostname.

Internally I have Windows DNS that I could alter to reflect the new server IP in the event of a failover. Externally, I would just alter the NAT on the firewall.

Does anyone have any experience with this type of setup? Anything I need to be aware of?