About how Vault uses volume groups and pools
The volume groups identify where volumes reside. They are used as a tracking mechanism by Vault to determine where a volume is located. Volumes in a robotic volume group reside in a robot. During a Vault job, Vault searches the robotic volume group for the media that matches a profile's criteria. If media is found, Vault ejects that media and then moves it logically to an off-site volume group. A logical move means to change the volume attributes to show the new location. When a volume in off-site storage expires and is injected back into the robot, Vault moves it back into the robotic volume group.
Volume pools identify logical sets of volumes by usage. Vault uses them to determine if a volume should be ejected. Volume pools for images to be transferred off site are known as off-site volume pools. When you create the images that you want to send off site, write them to media in an off-site volume pool. During a Vault job, Vault searches a robot for the images that match the selection criteria. If the media the images reside on are in an off-site volume pool, Vault ejects that media.