Comment by beagle3
Individual writes are safe, in my Experience with thousands of uSB drives in many configurations, some with 12 2tb drives hanging on multiple USB hubs at the same time.
However, there are disconnects/reconnects every now and then. If you use a standard raid over these usb drives, almost every disconnect/reconnect will trigger a rebuild — and rebuilds take many hours. If you are unlucky enough to have multiple disconnects during a rebuild, you are in trouble.
I've had bitflips with USB transfers of 1-10TB. I don't remember the specifics, but my personal confidence in USB is low.