A. No. You can't have a mix of Server 2008 and Server 2008 R2 nodes in a cluster. You need to create a new Windows Server 2008 R2 cluster and then migrate resources from the Windows 2008 cluster. If you don't have new hardware, remove nodes from the existing cluster, rebuild them with Windows 2008 R2, then create a new cluster and migrate resources. Obviously, during this time of breaking the cluster, you have reduced your high availability, so you don't want to stay in this state long.

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