Linux-HA & Zimbra?
There is a product for HA clustering, called Linux-HA (http://linux-ha.org).
The simplest requirement from the application is to keep all data files
on the same (shared) partition (say, /cluster); engine will start/stop/restart
applications as needed.
It it doable with Zimbra? Please, do NOT refer me back to Red Hat Cluster
Suite, I can read product specs :-)
As you already figured out we've integrated and tested with Red Hat Cluster. Feel free to try something different. We've never tried that particular HA code but have had good success with Red Hat's cluster offering. If it works out for you please report back, as we'd be interested in your results.
(Almost) everything we install is under /opt/zimbra - the only exceptions are some system config stuff (ld.so.conf, sudoers, passwd/groups entry) so this shouldn't be a problem.