Earlier quoted context omitted.
You can buy a DAS (Direct Attached Storage) enclosure[1], some even support RAID. If your Nuc is multipurpose, you could then run a virtualized TrueNAS guest (BSD or linux) in QEMU and give it control of the DAS block device for ZFS pools. Being able to run a virtual NAS that actually gets security updates on demand is pretty neat - TrueNAS has an excellent API you can use to start/stop services (SMB, SSH, iSCSI, etc…
Isn't running a NAS on top of USB storage very strongly discouraged? TrueNAS cautions against it. I also want to set up a NAS on a mini-PC with some sort of attached external storage, but I haven't been able to get past this blocker. USB is the only external interface these mini PCs typically support.
You're right, and I don't recommend USB as the only backup solution. I an old eSATA enclosure - not sure if that's an improvement over plain USB - as a secondary backup and keep the device on long enough to complete)