When recovering an Active Directory forest, Recovery Manager for Active Directory Forest Edition adds the global catalog to the DCs that acted as global catalog servers before the recovery, provided that these DCs were successfully restored from backup.
If none of DCs that acted as global catalog servers before the recovery were successfully restored from backup, Recovery Manager for Active Directory Forest Edition adds the global catalog to the DC which was assigned the schema master role during the recovery.
To recover your Active Directory forest with the Forest Recovery Console, you can only use backups created with the Recovery Manager Console. In simple environments, it is advisable to have only one Recovery Manager Console deployed. However, this may not be possible in large distributed environments that spread across different physical locations connected by slow links. In this case, you can deploy several instances of the Recovery Manager Console in each main physical location to back up domain controllers there.
You can also deploy several instances of the Recovery Manager Console if you want to
This depends on the forest recovery method you choose for your environment. For more information about these methods, see Forest recovery methods.
The decision on how many domain controllers to back up (and, therefore, which method to use for forest recovery) depends on the factors like
With a large number (50+) of domain controllers in the domain and significant size (over 1 GB) of the Active Directory database, it may not be feasible to fully back up system state of all domain controllers in the domain due to storage limitations or time constraints. In this case, you can back up only some of the domain controllers.
A good practice is to back up at least two domain controllers in each domain in the forest. It is recommended to back up the domain controllers that are DNS servers and FSMO role holders.