• Hi,

    As per Microsoft website:

    You cannot upgrade the operating system of a clustered server from Windows Server 2003 to Windows Server 2008 or Windows Server 2008 R2 and from Windows Server 2008 to Windows Server 2008 R2

    Here is the link that shows you the proper was of doing it: http://support.microsoft.com/kb/935197

    When upgrading a SQL Server 2005 cluster to a SQL Server 2008 cluster, the installer will do its best to keep the instance online for as long as possible during the upgrade. To do this, when you begin the upgrade process, start on a passive node. If you attempt to start by upgrading the active node, the installer will prompt you to fail over the SQL Server instance to another node before proceeding. Here is a nice article on how to

    Upgrading a SQL Server 2005 Cluster to a SQL Server 2008

    at http://www.devproconnections.com/article/clustering/upgrading-a-sql-server-2005-cluster-to-a-sql-server-2008.aspx

    I hope I was able to help you.