Hi Cluster Fans,
Windows Server 2008 Service Pack 2 (SP2) is now available for download on the web! This blog post will walk you through performing a “rolling upgrade” from Windows Server 2008 RTM to Windows Server 2008 SP2. A rolling upgrade allows you to progressively upgrade your cluster nodes while keeping your resources highly-available, however you may have some downtime while moving the resource groups between nodes.
Source : Clustering and High Availability
