At a high level, the upgrade process involves the following tasks:

1. Take a backup of the SQL Server databases.

2. Upgrade SQL Server on the first cluster node.

3. Upgrade SQL Server on each additional failover node.

4. In case of a disaster recovery (DR) configuration, ensure that the databases on the primary site and secondary site are synchronized and then proceed to upgrade the cluster.

   You can upgrade the cluster using one of the following methods:

   • Add a temporary disk and create the volumes similar to that on the primary site.

     To follow this method, perform the pre-upgrade tasks and then proceed to upgrade the cluster on both the sites. You must follow the same upgrade sequence simultaneously at both the sites. Upgrade the first node and then upgrade the additional nodes.

     See Preupgrade tasks for upgrading SQL Server 2008 to SQL Server 2008 R2 in a disaster recovery environment.

   • Delete the SQL Server 2008 service group and then create the SQL Server 2008 R2 service group.

     Follow this method only if the data size is small. After you re-create the service groups and setup replication across the two sites, the entire data will be replicated. The replication takes a considerable amount of time.

     See Deleting the SQL Server 2008 service group and creating the SQL Server 2008 R2 service group.

5. Run the SQL Server configuration wizard in the modify mode to modify the SQL Server 2008 service group.