I'm in the process of refining a failover solution for our Zimbra Install (Network Edition). Right now, I'm testing a process of taking a sync of the Live servers Backup directory and restoring it to a standby system. (you can see a lot of what I'm doing in my sandbox page).
I do an incremental backup once every hour on the live system, rsync that across, then run a zmrestore -restoreToIncrLabel incr-XXXXXXX -a "all"
I have 60 accounts totaling about 25GB of total data. Now, if I do a restore to incr it takes about 2.5 hours on our standby machine (Dell P4 2.4Ghz w/1.5GB Ram). If I do another restore to incremental using the backup made just one hour later, it still takes 2.5 hours. So, essentially, it takes the same amount of time to bring it up to speed for one hour as it would for the entire system. Does this sound right?