Upgrading a data warehouse is always a problem. As the system becomes a victim of its own success, it will become harder and harder to find extended periods of time when the system can be down. This is particularly true if the server is in itself a complex environment, such as a cluster or an MPP box. Upgrading one of these systems is a major challenge in itself, even before you consider the database upgrade that this might enforce, and the code changes to the applications that may be required. Before upgrading the data warehouse you should upgrade the test system to ensure that the upgrade goes smoothly. You should also check that the versions of the operating system, the RDBMS and any third-party software are compatible.