NetBackup assigns an ordinal number to each copy of a backup image written by a backup policy. That number designates its sequence of creation. NetBackup also designates one of the backup images as the primary backup copy. The first backup image created successfully by a NetBackup policy is the primary backup; if only one copy of a backup image is created, it is the primary copy. NetBackup uses the primary copy to satisfy restore requests.
Usually, Vault duplicates from the primary copy, whether it exists on disk or removable media. Exception: for improved performance, Vault duplicates from a nonprimary copy on disk if one exists and the primary copy is on removable media.
Because both NetBackup and Vault use the primary copy, in most circumstances if a primary copy is on removable media it should remain in a robot. If the primary copy is off site, you cannot duplicate the image until the media is injected into the robot or a local copy (if available) is promoted to primary. (Exception: Vault duplicates from a nonprimary copy on disk if one exists.)