I know it's an old thread, but :
On the issue of backups:
Search for zmbak_v.0.8.sh script. Works very well. Not most efficient i.t.o. storage space, I modified it to FTP backups every night to a Windows PC running free FileZilla FTP server. Does weekly full and daily incremental.
On the issue of live sync: Howto: Highly available Zimbra cluster using Heartbeat and DRBD | green bee digital
Is 1 example of how to use DRDB & Heartbeat with Zimbra. I use it to run a Zimbra 6 physical server that DRDB/Heartbeat to a virtual server in case things go pear shaped. Saved my butt once already. Works very well, but stock up on coffee as it will take a while. Initial syncing takes forever...