If you need 24/7 availability then you need to go to the Network Edition.
As I said the fastest backup you can get with the open source edition is if you installed Zimbra on an LVM partition in which case you can get your backups down to the same time it takes to run this:
Code:
zmcontrol stop; zmcontrol start
But that is the smallest downtime you can get for the open source edition.
One option you might look into is setting up Zimbra on a
DRDB or similar setup, but this is quite complex to setup. There are a few threads in the forum about it.