The correct PowerShell cmdlet to use to add a virtual hard disk (VHD) to an existing virtual machine (VM) in Windows Server 2012 is the Add-VMHardDiskDrive cmdlet.
Here's an example showing its use on IDE:
Add-VMHardDiskDrive -VMName -ControllerType IDE -ControllerNumber 0 –Path "" -ComputerName
To read more on the Windows Server 2012: http://www.windowsitpro.com/windows-server-2012
