Before upgrading the databases, you should check them for errors that can prevent a successful migration. It is recommended that you run database integrity checks against all of the databases with the DBCC CHECKDB, DBCC CHECKCATALOG, DBCC NEWALLOC, and DBCC TEXTALL commands. In the event that database inconsistencies are found, you must repair the database or restore to a clean one before you begin the upgrade process. You should then back up the SQL Server 6.x installation, including the master, model, and msdb databases, as well as all of the user-defined databases. Also, you may want to back up the actual data and log files. Perform any repair or restoration work after all production activity has been stopped for the upgrade, and the DBCC consistency checks have completed successfully.