I think that if you install with the 80gb, and then add the 1 tb, that if you don't start copying anything to the server until after the 1tb is installed, then everything will go to the 1tb drive. However if you turn folder duplication on, then it
will definitely cause the duplicate folder to be on the 80gb drive, because you need 2 physical drives for folder duplication. With a 3 disk setup... IE 80, 1tb, 1tb, then it should never use the 80gb drive.
One addon that you will definitely want to install on your WHS is the Disk Management addon. It will let you create a wireframe diagram of your server, and it will also tell you how much data is stored on each physical drive. Unfortunately it's
$10, you might be able to find an older version of this addon which was originally free. But there is a 30 day trial available, which might be good enough to just check it out.
http://www.tentaclesoftware.com/products/whs/diskmanagement
Here is an image of what that looks like:
http://geocline.net/miscimages/WHS(BENDER)_DM_21-09-08.png
_DM_21-09-08.png){kind=link}