I’m running my trusty old Antec 900 with three Rosewill hotswap bays to hold 12 3.5” drives.

gamersnexus.net/…/goat-antec-900-case-revisit-new…

www.newegg.com/…/N82E16816132037

I’ve got this laying on its side currently, and I need to replace the failed top exhaust fan, but I’m sure you could come up with a rack mount option to throw it in a rack. Probably about 4u tall on its side.