Hi first format usb to Fat32 on computer.Turn off box insert usb and turn box on.Go to settings/storage devices select your usb drive and set to no standby..
then select initialize okay it and then when completed reboot box.recording paths are already set to media/usb as default in vix so you should be ready to go.Dont forget to set up epg as well once drive is good.
If you continue to have problems i found the only way to sort it proper was to reflash box when flash is complete before reboot insert formatted usb or keep it in box while flashing and off you go..if this dont sort it get another usb drive.