(I work at fb)
That video's discussing btrfs layering, which is very neat.
I am _very_ curious what sort of experience FB has had with btrfs.
If FB has decided to go all-in with btrfs, you probably have the most accurate raw data there is to have.
Of course, any hyper-scale deployment of a technology is going to produce remarkable/exponential statistics, and these will (sadly/annoyingly) need careful parsing to normalize in a way that is generally accessible and unsurprising. (We live in a very knee-jerk world, and all. Sigh)
All this to say, I at least am looking forward to whatever sorts of numbers you end up being able to share.
After considering the bit about btrfs in the video, and your mention of "1 or more machines", I wonder if you aren't using btrfs on things like load balancer type systems - or, more abstractly, node configurations that can always safely be "thrown away", whether by hardware failure or explicit decommission. But then I realize the chances are you probably use such a model (individual hardware failure must be acceptable; everything important must be n-way redundant) because nothing else makes sense at scale. And then I wonder... exactly what point in that spectrum does btrfs fit in? I wonder if/how you can answer that question.