I'm often asked whether you need to install Exchange Server 2010 RTM first, and then install Service Pack 1, or if there is a way to install SP1 in a single operation.
After an outage or maintenance to the Mailbox servers in a Database Availability Group you may find that the mailbox databases are no longer balanced across all of the DAG members.
When an Exchange Server 2010 Database Availability Group has been upgraded to Exchange 2010 SP1 you may encounter an error when adding or removing database copies on a DAG member.
Microsoft has released Exchange Server 2010 Service Pack 1. Organizations already running Exchange Server 2010 (RTM) can upgrade to Service Pack 1, however the upgrade must be planned out properly to ensure a successful outcome.