Just for fun, I tried updating the firmware so that our existing SCSI card would support mirroring. That did not work, so hardware RAID is off the table for now.
In this case, given the limitations of the card, hardware RAID would have been less desirable anyway, perhaps, because the card only supports 0 and 1, not 5. This would limit us to 36GB of disk space.
With software RAID, we can do RAID 5, so that our 3x36 can work as 72GB.
So, I think that's what we should do.
--Jimbo