A pass-through disk that is assigned to a virtual machine is not migrated when you upgrade to Windows Server 2008 R2

Consider the following scenario.

• You have a server that is running Windows Server 2008 and that has the Hyper-V role installed.
• You have a virtual machine (VM) stored on the server that has a pass-through disk assigned to the VM.
• The pass-through disk is online in the parent partition. Or, the pass-through disk is offline and physically disconnected from the server.
• You upgrade the server to Windows Server 2008 R2.

In this scenario, the pass-through disk that is assigned to the virtual machine is not migrated in the upgrade to Windows Server 2008 R2.

This issue occurs because the virtual machine-specific Discretionary Access Control List (DACL) for the pass-through disk is migrated in the Setup program for Windows Server 2008 R2. If the pass-through disk is online in the parent partition or is disconnected from the server during the upgrade, the DACL is not migrated.

To resolve this issue, use one of the following methods, as appropriate for your situation.

Method 1: The pass-through disk is online in the parent partition during the upgrade

1. Open Disk Management. To do this, click Start, type diskmgmt.msc in the Start Search box, and then press ENTER.
2. In the right-side pane, mark the pass-through disks as offline. To do this, right-click each disk next to its disk number, and then click Offline.
3. In Hyper-V Manager, right-click the affected virtual machine, and then click Settings.
4. In the navigation pane under Hard Disks, select the entry that was used for the pass-through disk.
5. In the Physical disk box, select the disk number for the offline disk that has to be reattached to the virtual machine.
6. Turn on the virtual machine. The correct DACL is used for access by the virtual machine.

Method 2: The pass-through disk is physically disconnected during the upgrade

1. Reconnect the pass-through disk, and then confirm access from the parent partition.
2. Follow the steps in Method 1 to mark the pass-through disk as offline, and then reattach the disk to its respective virtual machine.