it's different at scale, and you mostly don't need SSDs since you have cache boxes, most your storage is videos that are very rarely used. You're looking at pro

it's different at scale, and you mostly don't need SSDs since you have cache boxes, most your storage is videos that are very rarely used. You're looking at probably a rack of SSDs for every 5-10 racks of spinning disks X 3 datacentres. Even that would give you approx 50-90PB of usable storage (replicated so it's in all three sites) for a few tens of thousands a month. Even if you just put it all on S3 infrequent, which would be one of the most expensive ways of doing it, it's still not really expensive compared to serving the content.