Okay, so if this is a professional gig, then off site backups are a must, and raid on site is also. But for a pro photographer I'd have expected disk costs to

Okay, so if this is a professional gig, then off site backups are a must, and raid on site is also. But for a pro photographer I'd have expected disk costs to be a necessary expense. In Australia we have 10TB disks for AUD 450. Double up for redundancy and add on chassis, this isn't trivial $s, but equally it's presumably 'worth it'. For my non-pro and far more modest collection of around 300GB of images, I keep copies on three local machines, and one remote (family member) with sync changes being able to be done over home grade ADSL. With your volumes you could do off site sync via usb disk easily enough for new large ingests, and propagate smaller changes over the wire. Having a friend or family in the same city is very convenient compared to trying to hunt down the best all you can eat deal du jour, with no need to handle the regular t&c changes those services suffer. Good reciprocal opportunities too, of course.