A cautionary note for those of you performing an in-place upgrade of a machine running Windows Server 2008 with the Hyper-V role enabled, to Windows Server 2008 R2 Release Candidate.
During the installation, you will see the following compatibility report message stating that you should turn off the Hyper-V role:
This warning is incorrect, and you should not do this as the virtual machines will not be present, and virtual network configuration will be lost once the role is re-enabled.
You will see a similar message if you have virtual machines running at the time of upgrade, but it is a “hard block” (in other words, you cannot proceed further). In the case where you hit the hard block, running VMs should be cleanly shut down prior to upgrade. However, I re-iterate, you should not remove the role itself.
One other point to note is if you have online snapshots or virtual machines in a saved state. Saved states are not compatible between Hyper-V in Windows Server 2008 and Windows Server 2008 R2 RC build, so you should ensure you cleanly shut down VMs and delete online snapshots prior to upgrading to avoid the following message after the upgrade is complete: