You take a drive offline to remove or change the tape cartridge. This operation rewinds the tape cartridge and ejects it from the tape drive. The device is still available to the system, but is not ready for I/O or tape movement.
You use a urst tape device to unload and reload a tape cartridge during a backup or restore operation. When you use a urst device, Data ONTAP waits for you to insert the new cartridge before continuing the operation. However, when you want to remove the current cartridge when no other operation is ongoing, you must use the mt offline command with an nrst tape device.