1. Arch Linux Wiki (https://wiki.archlinux.org/)
2. Arch Linux man pages (https://man.archlinux.org/)
3. FreeBSD Handbook (https://docs.freebsd.org/en/books/handbook/)
4. FreeBSD man pages https://man.freebsd.org/cgi/man.cgi
5. https://vermaden.wordpress.com/
6. https://klarasystems.com/articles/
7. https://openzfs.github.io/openzfs-docs/
8. https://btrfs.readthedocs.io/en/latest/

These are only the resources that come to mind in a couple of seconds. Will update them later 🙂