Consumer external hard drive enclosures may offer a JBOD mode, I had one from Icy Box for a few days, the transfer rates were good but the little fan didn't cool the hard drives well enough while accessing them. Ended up buying a Define R5 instead
BTRFS + Seagate SMR seems to work well in my experience, especially if used like a WORM drive. No 24/7 rating, but 5TB per drive
Consumer external hard drive enclosures may offer a JBOD mode, I had one from Icy Box for a few days, the transfer rates were good but the little fan didn't cool the hard drives well enough while accessing them. Ended up buying a Define R5 instead