You can create partitions for robotic library slots to control which media is used for backup jobs. After you create the partitions, you can submit jobs to those partitions’ device pools.
The partition device pools appear under Robotic Libraries for the robotic library on which they were created. All partition device pools for a robotic library have the same name and display the slot ranges for the partition in parentheses within the name.
See About robotic library partitions.
To create robotic library partitions