I just restored my Server 2012 install from a 1TB volume to a 2TB volume. I wanted more storage and it was a better RAID controller. Trouble is, while the partitions are still all the same size and add up to (roughly) 1TB, the OS is somehow showing that I am using all of the 1.8TB of the new volume and won't let me expand any disks to take advantage of the new space. I don't know what went wrong. I was going to try to boot from another disk and try to examine the disks more closely, but I was hoping that I am simply missing something obvious.
Look at the attached image to see what I mean. The volumes all add up to about 900GB (the blacked out one is a USB-based backup volume), but the OS still thinks that all 1.8TB are being utilized. Little help?