If you’ve got an empty header on the motherboard you can get adaptors to make it a normal USB A slot inside the case or a slim profile usb stick. There’s a list of recommendations on their forum.
I ended up getting a Dell raid card that I flashed to a normal HBA/IT mode and connecting all my disks with that in a big case.
Happy experimentung. Hopefully you’ll find something that fits your needs.
Id go with what ever you’re comfortable with supporting, but a few comments.
Truenas core is bsd, Truenas Scale is Linux based. Truenas/ZFS needs direct access to the disks. you should not run it with hardware raid. Unraid loads the OS mostly to ram and the serial number on the usb stick is used for licensing.
I saw someone else summarise it as if you care about easy to use and setup apps use Unraid. If you care more about your data use Truenas.
A few sandwiches short of a picnic.
TS being worked on next http://www.openra.net/about/