*** Disclaimer *** -- The following is just my own personal opinion.
I wouldn't worry too much about running on CentOS. A LOT of people here in the forums (including myself) run under CentOS. Of course I'm running the FOSS version, but I know there are several installs running the Network Edition under CentOS as well (including at least one moderator -- it's in his profile). If you are familiar with Linux you probably know that CentOS essentially IS an "un-branded" version of RHEL. I think the reason it is not officially supported has more to do with things of the political / business nature than anything else. I just wanted to point it out because if you are going to tackle the upgrade / migration and you run into issues where you want to call support you may run into some resistance. (Other NE / CentOS users/admin can probably speak better to this point.)
As far as your OS upgrade, I suppose you could backup your Zimbra installation (double and even triple checking that you've got a good backup) then wipe out your CentOS 4 and do a fresh install of CentOS 5. You can probably find several posts here and elsewhere of people who did in-place OS upgrades and had no problems. I'm just not comfortable with it myself.  |