Just completed a migration from Ubuntu 8.04 to RHEL running virtually. Moved from 4 to 2 processor cores, but everything seems to be up and running.

Used rsync and Followed:
http://wiki.zimbra.com/index.php?tit...es-Server-Move

Had some issues with permissions mapping due to different IDs, but chown -R on /opt/zimbra and continuing with the instructions fixed all that.