I knew about library genesis by 2012. It was at least 10 TiB large by then, IIRC. With the amount of Russian language content I got the impression it was more popular in that sphere, but an impressive collection for anyone and not especially secret.
To be fair, he might have been rather preoccupied at that time.
Is lib still around anymore. I can't find any functioning urls
It's in the megathread linked in this comment, but I want to specifically point to https://open-slum.org/ which is basically a status page for different sites dedicated to this purpose, and which I've found helpful.
Lol. I opened that link and was like "hmmm, that UI looks familiar".
Life pro tip: the Wikipedia pages for Libgen and Scihub contain up-to-date current links in the right sidebar. Only for the purpose of information and documentation, of course.