One thing to note; I noticed when I was creating this that the "Available Space" column did not show in my initial report. Check your column widths! (Took me a few minutes to see that the default for the report is 'Custom')
This is from http://oriondemo.solarwinds.com/ to ensure it is the default report that comes out of the box (except for the last pic as I needed some live data):
Original Results (after following all of the steps outlined above)
Step 1 - Edit the column widths
Step 2 - Set you widths so that you can see the far right "Available Space" column (I went with 'Automatic')
Final Result:
