Did you try installing on a single spindle then Carbon Copy Cloning that to the RAID 0 pair on the external?
Since Snow we haven't been able to directly install OS X onto RAID 0 setups, we had to clone, don't know how that's going to work with Lion, since you've upgraded it on a pair alreaddy likely means it still works.
Yes, I used Carbon Copy Cloner with the operating system on MacBook Pro's internal drive as the "Source" and the the single Fantom external drive, as well as the CalDigit dual Raid 0 external drive, as the "Destination".
CalDigit still wouldn't boot. Fantom drive still only booted via USB 2.0, and only off the left USB port.
Powered drive, not port powered?
Mac''s have been cutting them off if they drain too much.
I have no problem booting off cloned drives, 10.6.8.
I haven't heard of any screaming death threats concering Lion not booting off a clone, so I assume all is well there.
I can only think it's something wrong with the ports, since you've used it like that for quite some time, perhaps they are worn out?
Both the Fantom and CalDigit have their own power source.
Interesting thought that the ports might be worn out from overuse. But my Macbook Pro is still running off the original set of striped Fantom drives. So the port still works. Just not with a newly "blessed" drive.
I never use the Firewire 400 port and that doesn't work either.