Comment 35 for bug 433438

FWIW, I only see this with LaCie external drives, over USB. From tragic experience, I know the USB connections on those drives to be prone to failure, often leaving only the FireWire ports functional. For some reason, the same drives still work on Macs.

So, could be buggy USB devices and/or bad cables, but clearly something could be done to make Linux more forgiving, since Windows can connect to such drives on the same machine (per reports of others, haven't tried myself).