In the case of a disaster where the data center is no longer available, which...

In the event of a disaster where the data center is no longer available, the first step should be to activate the call tree1. A call tree is a layered hierarchical communication model used to notify specific individuals of an event and coordinate recovery efforts1. This ensures that all relevant parties are informed about the situation and can begin executing their parts of the disaster recovery plan1.

References:

IT Disaster Recovery Plan | Ready.gov