This information is included in the DeltaV Backup and Recovery documentation but is worth pointing out here as well.
A domain controller running Windows Server 2003, Windows Server 2008, or Windows Server 2012 relies on Active Directory, a security service responsible for enforcing security policies and for authenticating users and computers within a domain network. The domain controller tracks objects in an Active Directory database based on their Update Sequence Numbers (USN). USNs are replicated to other domain controllers in the network. Recovering a domain controller can result in its having an Active Directory database that is out-of-synch with replications stored on other domain controllers in the network. This dilemma is referred to as a USN rollback condition.
Some precautions are recommended to avoid encountering a USN rollback when recovering a domain controller or its Active Directory database. At a minimum, perform the following precautions when backing up a domain controller:
For example, if the tombstone lifetime is set to the default minimum, 60 days, back up the domain controller at least once a month.