It turns out the problem was just a bent pin on the SCSI cable, likely from having to stretch things a bit to reach optimus from the RAID unit.
I hooked it up to megatron, and it was automatically recognized and mounted.
I had to turn off the new FB machine and remove it from the rack to be able to access megatron though, since it was just sitting on top. FB needs a rail to sit on!
At a cursory glance, the filesystem appears intact. I have copied over the achived DRFPMI frame files to my user directory for now, and Gautam is going to look into getting those permanently stored on the LDAS copy of 40m frames, so that we can have some redundancy.
Also, during this time, one of the HDDs in the RAID unit failed its SMART tests, so the RAID unit wanted it replaced. There were some spare drives in a little box directly under the unit, so I've installed one and am currently incorporating it back into the RAID.
There are two more backup drives in the box. We're running a RAID 5 configuration, so we can only lose one drive at a time before data is lost.