By "fairly rickety", I mean a pair of 4-bay Vantec enclosures connected to a USB3 hub, connected to a laptop, with a single USB3 port, running Ubuntu, in a tiny unventilated closet.
Given how vastly more reliable these enclosures were than the hideously awful bit-flipping mess I originally got from MediaSonic for this purpose (DO NOT BUY THIS), I thought that the Vantec was actually a pretty good deal.
But nevertheless the Vantec enclosures behaved… suspiciously. Particularly, in certain situations, they would start spuriously disconnecting drives all the time.
(If anyone has a suggestion for an actual reliable thing for putting non-trivial numbers of disks onto a USB3 bus, I'd like to hear about it.)