Well, this looks like as good an excuse as any to test the new Firewire port I wired into my computer recently.
You know you're really lazy when you need an excuse to move an external hard drive across the room to test something.
Oops, the cord doesn't reach. [Yawn] Oh well, I'll test it later...
I know, I'm pathetic.
Anyway... I got off my lazy butt and moved the drive to my tower to try my newly wired front Firewire port, and... it works! So it looks like Firewire works under Cassandra. The drive auto-mounted and appeared on the desktop. I'm watching an episode of Battlestar Galactica off the drive as I type.
Of course this doesn't help you solve your problem. Sorry. But at least we know Cassandra works with external IEEE1394 "Firewire" hard drives (and my new front port works!).
Only thing I can think of at the moment... was the drive connected when you installed Cassandra? If so there may be an fstab entry for it that is preventing Mindisk from mounting it. Mintdisk will not mount anything referenced in the fstab file (even if it is commented out). If there is an entry in fstab for the firewire drive, remove the entry, reboot and try again. If not, then, I dunno...
PS: I can fix the double icons, though. Go to Control Center, System, minDisk and uncheck "Show links for mounted partitions" and restart. You should only have 1 icon per drive now. The reason you get double icons is that mintDesktop and mintDisk are both putting icons on the desktop. It's best to just let mintDesktop handle that.