An in-place upgrade is the quickest and simplest upgrade method because
· It upgrades all system and user database objects and settings for you.
· Client applications do not have to be updated to connect to a new instance of the relational database engine.
However, an in-place upgrade is an all-or-nothing approach. In the unlikely event that an in-place upgrade of the relational database engine fails, you cannot quickly roll back to SQL Server 2000 or 7.0 once the setup program finishes. There is a go/no-go point within the setup program before which you can simply cancel the upgrade. After this point, to roll back to SQL Server 2000 or 7.0 you need to
1. Uninstall the SQL Server 2005 database engine.
1. Reboot.
2. Reinstall the previous version of the SQL Server database engine.
3. Restore the system and user databases from database backups.
Downtime in the event of upgrade problems can be significant.
With an in-place upgrade, SQL Server 2005 Setup installs SQL Server 2005 on the server, switches the source SQL Server instance's services over to the new SQL Server 2005 instance, upgrades the databases in place, and then removes the SQL Server 2000 or 7.0 binaries. All system and user databases are upgraded along with the relational database engine. During actual database upgrades, users will not be able to access any relational databases on the SQL Server 2005 instance. After the in-place upgrade is complete, only the SQL Server 2005 relational database engine will remain. With an in-place upgrade, the upgraded databases and the database engine can be tested by the database administrator only after the SQL Server 2000 or 7.0 relational database engine is removed.