Practice volumes
You can use a practice volume to practice what you would do in the event of a disaster, without interrupting current data replication. Practice volumes are available in Metro Mirror, Global Mirror, Metro Global Mirror, and Metro Mirror - Global Mirror sessions.
To use the practice volumes, the session must be in the prepared state. Issuing the Flash command against the session while in the Prepared state creates a usable practice copy of the data on the target site.
Note: You can test disaster-recovery actions without using practice
volumes. However, without practice volumes, you cannot continue to
copy data changes between volumes while testing disaster-recovery
actions.