Windows Server 2012 VM shows RDM disk offline

Hi -

Hoping someone can help me here. I created an RDM disk from a 1TB SATA disk I have in my ESX 5 machine. No issues creating the vmdk file, and I can add the VMDK to a Windows 7 guest I have, and it works without issue. But when I add it to my Windows Server 2012 guest, the disk shows up in disk manager, but shows "offline" and I can't seem to do anything with it. Anyone have any ideas on how I can get this to show up properly in my Win2k12 guest?

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Thanks in advance for any help!