Have you created a share on “Extended Volume?” There is no default share created when in this mode, so you have to do it manually. Once created, it will appear as another item in Finder or Network Neighborhood.
Just in case you or someone else doesn’t know, here’s how to create the new share.
browse to the Basic Mode - Folder Shares page
enter the name and description for your share
choose “Extended Volume” from the volume drop down box
click submit
You should now see the other 1TB of your two mirror setup.