I just finished reading this post; https://www.experts-exchange.com/questions/28159047/Correct-partition-sizes-for-physical-servers-running-Windows-Server-2012-Standard-Hyper-v.html
and although it is very similar to my situation mine is slightly different. I have just received a Dell T320 with 4 1TB drives configured in a RAID 5. OS was pre-installed by Dell. They used BIOS instead of UEFI to install Server standard 2012 so 2.2 TB limit applies. They configured 2 discs; 0 is 1.8 TB, 1 is 950GB. disc 0 was 3 volumes; system 3 GB, C:\ 40 GB and E:\ balance of disc. Just to be clear no VMs are installed yet.
C:\ had 5 GB free so I deleted E:\ volume to create free space on disc 0. I then attempted to expand C:\ but failed, error message is Extend Failed. (gosh that was informative). I checked in Administrative Tools >> Computer Management >> Disc Management, disc 0 indicates unallocated space.
Dell support claimed that C:\ is locked and can't be extended. I tried G-Parted but it didn't see the volumes. Any other ideas before I re-install the OS?