Hi. I get what a Drobo does with it's BeyondRAID configuration. It's great protection against a single or dual hard disk failure. But it doesn't protect against theft, fire, firmware failures or human error (inadvertently deleting a file). So the data on the Drobo still needs to be backed up (say, nightly) onto a large capacity external drive, correct? Is there a USB or other port on the Drobo to connect an external drive for back-up? Thx