The Pockettec usbdisk wouldn't come up. Eventually, I removed it and connected it to "flux" in the dorm. It didn't mount (though it may have been fine anyway), but I went ahead and used fdisk to rewrite the partition table (that I hadn't changed) and then checked with fsck. Finally I manually mounted it to "flux" and it was fine. I replaced it in M21 and it started up without further difficultly. <Perhaps> it was a connector issue, but I'm not sure.