[dnanian]

It sounds like your FireWire drive failed during the copy process. When this happened, it partially unmounted without telling SD!, so SD! kept copying. If you detach the drive and look in /Volumes, you'll see a folder named the same as the drive ("Disk Images", I assume). That needs to be removed.

It sounds to me like your FireWire subsystem isn't necessarily reliable enough to support this kind of activity. You can try backing up again, but I'm concerned that things are flaky enough to prevent proper operation. I'd suggest trying to simplify the FireWire bus as much as possible: only attach the external drive, nothing else, then Smart Update the backup.