It's often important to keep track of the size of your partitions. I've created a simple script that will report the size of each of your partitions. This script requires SQL Server 2008 R2 or greater on the server as well as SQL Server 2008 R2 Management Objects & Windows PowerShell Extensions for SQL Server on the machine running the script. There is a handy guide to this here.
This script runs remotely so it may take a while to run. However I have run this script on 11.5TB of data and it returned the result overnight.