Apparently, in 2017, that was somewhere around 16 terabytes. https://www.theregister.co.uk/2017/05/16/aws_ram_cram/ Heck, you can trivially get a 4TB instance from Amazon nowadays: https://aws.amazon.com/ec2/instance-types/
The biggest DBs I've worked on have been a few tens of billions of rows, and several hundreds of gigabytes. That's like... nothing. A laughable start. You can make trivially inefficient mistakes and for the most part e.g. MySQL will still work fine. Absolutely nowhere near "big data". And odds are pretty good you could just toss existing more-than-4TB-data through grep and then into your DB and still ignore "big data" problems.