Your colo facility will almost certainly have 24/7 staff on hand who can help you with tasks like swapping disks from a pile of spares, but expect to pay $300+ minimum just to get someone to walk over to your racks, even if the job is 10 mins.
With that said, the cost savings can still be enormous. But know what you're getting into.
If you do a 60-disk 4U setup you'll need 1 full rack of those just to get your 10PB, then you'll need yet another one for redundancy. And then a quarter for hot spares. At that point you have single-redundancy, no file history and no scaling. Is it possible? Sure. Is this something you can do 'on a side track with the people you already heave'? Unlikely if you are a startup with no datacenter, no colocation yet etc.
They whole solution wasn’t cheap though and all of these extras were baked into the cost. We were getting better than S3 costs from a per TB straight up without considering power , cooling and rack space costs. Network was significantly cheaper than AWS.
Not sure on how far these NAS’ scale but I would expect deep discounts for something of this scale.
