Comment by beala

Yes I should have specified that this advice is specific to RAID configurations in NAS applications.

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...