He wants to rent something temporarily, so that he can copy stuff off the drives, take them out of the nas, format them in the new nas so it's compatible, copy stuff off the rented appliance to the new nas, ship the rented thing back off.
He wants to avoid having to have to buy enough drives, etc, to hold all of the data at once
He wants to avoid having to have to buy enough drives, etc, to hold all of the data at once