> /dev/usb/ep4.0 lun 0: inquiry Generic Flash Disk 8.07 geometry 8007680 > 512 > > ... so I'd think this is ok ...
My next step would be to get more diagnostic output from usb/disk. This is no longer easy with the new monolithic usb driver architecture. You can't just start 'usb/disk -d' because the usb/disk embedded into usb/usbd will have started automatically and seized control of the device when you plugged it in. I think you will need to generate a new usbd with the disk driver configured out (see /sys/src/cmd/usb/usbd/usbdb), then kill the usbd which is embedded into the kernel and start your new one, before running usb/disk.
