I can give you a couple insights:

300 hours of video are uploaded to youtube every minute in 2018

A couple of years ago I've seen a Google talk with a youtube admin/engineer. He said that in the beginning they had huge issues because they could not order servers fast enough for the demand. Money seems to never have played a role in those decisions (I can't find the link to the talk anymore).

If a video gets uploaded it will be stored in multiple resolutions and formats. So a video is probably stored as ~20 files which makes the space requirements even more mind boggling.