Update-DatabaseSchema cmdlet

The Update-DatabaseSchema cmdlet is designed to safely upgrade database schema in a DAG deployment. Unlike previous releases, a database schema upgrade in Exchange 2013 can only occur after all DAG members are upgraded to a version of software that supports the schema version and there is control over when the schema upgrade occurs. This design prevents issues like those encountered during upgrades of Exchange 2010 DAG members that automatically upgraded the database schema version when mounting database on an upgraded server and prevented you from being able to mount the database on a server that has not yet been upgraded.

More Reading: Microsoft Exchange Team Blog
Cmdlet Information: Update-DatabaseSchema