Can you give a little more details on how the enclosures work? Do you see each drive individually, or does each enclosure show as one "drive" which you then put into a zfs pool.

I'm looking to retire my power hungry 4790k server and go with a mini pc + external storage.

Replied to another comment with my setup - I use a QNAP JBOD enclosure (TL-D800S) connected to a mini-itx PC. (You do need at least one PCIe slot.) Shows up as 8 drives in the OS, the enclosure has no smarts.

I wouldn't do USB-connected enclosures for NAS drives - either SATA via SFF, or Thunderbolt.

In my case, each drive shows up individually. I create a new vdev encompassing all of them.

Each drive shows up as an external USB mass storage device?

I don’t know if it’s USB mass storage. It just shows up as separate devices in lsblk.