What kind of footprint would a system of this nature require I wonder? Geographically speaking.
It can be more/less than this depending on your rack configuration and how big drives you use, and how dense you pack them (e.g. "standard" off the shelf servers typically peak at 24 3.5" drives per 4U, while top-loaded specialised storage enclosures reach about 50 x 3.5" drives per 4U; full racks vary between 42U and around 47U etc.)
But you could if you wanted to get this much storage into about a 5m x 5m server room....
Of course you wouldn't, since you'd want multi-datacentre redundancy etc. Often there's also no point using the biggest drives available because you need higher throughput. Or no point packing them as tight as possible because you need more processing power per drive.