1. A method, comprising: mirroring a data set served by a primary storage system onto a backup storage system; storing one or more external configurations of the primary storage system on the backup storage system, the external configurations used to describe one or more instances of resources available on the primary storage system; determining unavailability of the primary storage system; and serving the mirrored data set from the backup storage system in response to unavailability of the primary storage system by using the stored external configurations of the primary storage system to assume the identity of the primary storage system.