Sharepoint Upgrade Process Overview
Two upgrade approaches are available for upgrading from Microsoft Office SharePoint Server 2007 to Microsoft SharePoint Server 2010 which are (i) In-place upgrade and (ii) Database attach upgrade. In-place upgrade lets you move all the Microsoft SharePoint sites on the same hardware but the database approach lets you move your content to a new farm or a desperate hardware. In addition, you may reduce downtime by merging up the In-place and database-attach upgrade.
In place upgrade enables you to install SharePoint Server 2010 on the same hardware, preserves your farm settings and makes customizations available after the upgrade. During the In-place upgrade, websites are available after the upgrade process whereas, in database attach upgrade, you will be allowed to upgrade content on a separate farm but you will not be able to upgrade any of the farm settings. You may upgrade multiple databases at the same time or upgrade them in any order that you want. This approach lets you combine several farms into a single farm. The database-attach approach is beneficial if you want to change your hardware or need to reconfigure your existing server farm topology during the upgrade process. With this approach, you detach the databases in your old farm and while you attach them to a new farm, the upgrade process runs and upgrades the entire database. This process is performed manually in a separate environment.
Plan your Upgrade Process