It is not necessary to delete drives from a cascaded drive pool before you delete that pool; the drives are automatically removed from the pool when the pool is deleted.
If scheduled jobs are assigned to the deleted cascaded drive pool, you are prompted to redirect them to another device or drive pool.
To delete a cascaded drive pool
Under Cascaded Drive Pools, select the drive pool or pools that you want to delete.
When prompted, click Yes or Yes to All to delete the cascaded drive pool or pools that are displayed.
If scheduled jobs are assigned to the deleted cascaded drive pool, you are prompted to redirect the jobs to another device pool or stand-alone drive.
If scheduled jobs are assigned to the deleted cascaded drive pool, you are prompted to redirect the jobs to another destination.
More Information
Retargeting a scheduled job from a deleted device pool or media set