Once you’ve added a new hard disk to Windows Server 2012, you’ll notice that it’s not showing up as a new drive in My Computer. To add a new hard drive to Windows Server 2012, do the following:
Open Server Manager
Click on File and Storage Services
Click on Disks
Right click on the new hard drive that you’ve just added
Click Bring Online, and click Yes
Next, right click on the new hard drive and click New Volume
Go through the wizard to allocate a drive letter to the new hard disk