How to format a disk for use as a bootbable backup?

Hello,

I am ready to migrate my iMac from Leopard to Snow Leopard.
I have a copy of Carbon Copy Cloner and a spare drive with enough capacity to make a bootable clone of my Macintosh HD, prior to starting the upgrade.

So, I started CCC and selected the Macintosh HD volume as a source, and selected the external hard drive as a destination.
The External drive is formatted as "MAC OS Extended Journaled".

As I went to start the clone process a window popped up telling me that I may not be able to boot from the Drive as some format's need to be applied.

I tried the process again, and the warning no longer appeared. I cancelled the process as I wanted to be sure this drive will be bootable.

Are there any actions I should take prior to starting CCC and letting the copy run? Is there any formatting I need to apply to the external drive?

 

old wiz

Well, I managed it the end, and have tested that the system can boot from the external drive. Thanks four your help.

Now ready to upgrade... once the SL disk arrives...