Although as an Exchange administrator, there shouldn't be many occasions on which you have to manually mount or dismount a database, sometimes you might be required to intervene because of an issue. The most common case is probably when a disk on which a database or logfiles are stored runs out of disk space. To protect the database, Exchange will automatically dismount the database. To recover from this situation, the administrator must free-up some space and manually re-mount the database. Therefore it's not only important to know how to perform these actions, but also to understand what's happening when they are executed.
In order to execute the following steps, you will need to log in to the Exchange Management Shell.