I hate blanket recommendations like this by docs. To me, it just sounds like some guy had a problem a few times and now it's canon. It's like saying "avoid Seagate because their 3tb drives sucked." Well they did, but now they seem to be fine.
If you're occasionally copying data to an external USB drive, that's totally fine. That's what they were designed for.
The issue is that they were not designed for continuous use, or much more demanding applications like rebuilding/resilvering a drive. It's during these applications that issues occur, which is a double whammy, because it can cause permanent data loss if your USB drive fails during a recovery operation. I did a little more research after posting my last comment and came across this helpful post on the TrueNAS forums going into more depth: https://forums.truenas.com/t/why-you-should-avoid-usb-attach...
Mainly I wouldn't do it because of there's space and SATA ports it seems stupid. Hotter. Worse HW.
Can't really see much good reason to do it tbh except it's in a small hot case which is relatively easy to move around. Maybe if you do occasionally backups and you don't care about scrubbing and redundancy? Otherwise why not shuck them and throw them in a case?
> 40-50tb total
> 8/12/16gb
How many drives are those?
You are kidding.