Question : Cannot use "Unallocated Space"

Background:
Dell NX3000 NAS Windows Storage Server 2008
I configured the 6 1TB drives in a Raid 5 configuration and installed the OS. Windows created a C: partition of 2TB and the remaining 2.6TB is marked as "Unallocated".

I shrank the C: partition to 1TB and created a E: drive out of the space left over from the shrink. I'm now trying to add the unallocated 2.6TB of space to the E: drive, but Windows will not allow me to do anything with the unallocated space. I can't even create a new drive. The only option I have is to view the properties.

Answer : Cannot use "Unallocated Space"

I resolved this by installing windows before I set up any RAID configuration on the RAID controller. After Windows was installed, I booted into the RAID controller and configured my array. The key was not to initialize the virtual disk during the configuration, but rather initialize it through disk management once I booted into Windows. This gave me the option to select GPT partition. I didn't have that option when I initialized during setup in the RAID controller.