20TB for me is at maximum shy of 60 hours of "decent"* quality video.
I shoot lots of uncompressed *QHD (720p) and 625 PAL footage. That takes up a LOT of space. 370GB/hour and 93GB/hour respectively. Yes, I am poor and can't afford a 1080p DSLR much less a Red 4k, yet I never delete a single frame. All that raw footage is copied twice, one goes straight into storage, one is the working copy, and the original stays on the camera until the production is finished.
I will burn a 2TB drive on a day's shoot without even thinking about it.
I'm not even going to try and estimate how much stock footage I have (several TB), never mind how many drives I have it on (a walk in wardrobe with a custom pop-rack and several dozen drives ranging from 200GB to 2TB). All I know is, I have a stack for personal use and a stack for work, and when a job comes in the first thing I do is buy a new drive for running backup. Pretty much guaranteed it'll get filled.