You can set a priority that determines the order in which the devices in a device pool are used. The default priority is 10 so all devices have the same priority initially. The device to which you assign the lowest number is the first device to be used in the device pool; for example, a device with a priority of 1 is used before a device with a priority of 5. You can set a priority of 1 to 99.
The Priority option is only displayed when you are viewing device properties under a device pool icon. Drives that are displayed under the Stand-alone Drives icon or the Robotic Libraries icon do not display a Priority option because the drive may belong to multiple device pools and have a different priority in each device pool.