ON new laptop, testing starting up from a backup OS, not working. Totally different in past. In past hold option on reboot and see drive options. Now really have to hold down power and option same time, to get the "Recovery" Module.
And then I think, remember, go into DU to see disc, there. I think my external OS backup was in there to do a reinstall (which did not do or need), but could not find or figure out how to just restart in that back up drive just see works. ie if can restart in it.