On an early 2009 24" iMac, part of my backup strategy is weekly SuperDuper backups to an external Firewire drive. The FW drive has always been a bootup option if I hold the "option" key when booting and I could run from the FW drive no problem. Well yesterday I had a system crash and was unable to boot to the iMac internal HD, and the FW drive was not visible when booting. I suspected a hardware failure but surprising was able to restore from a Time Machine backup (14 hours). After restore from TM I was again able to boot to the internal HD and the FW drive was visible again. So obviously my FW backup strategy failed, but why would a system crash make the external FW drive unavailable? Is that expected behavior if I lose the internal HD in the future? Should I not plan to boot to the FW drive if the internal HD fails?