The Jetstor RAID array is back in its nominal state now, according to the web diagnostics page. I did the following:

1. Powered down the FB machine - to avoid messing around with the RAID array while the disks are potentially mounted.
2. Turned off all power switches on the back of the Jetstor unit - there were 4 of them, all of them were toggled to the "0" position.
3. Disconnected all power cords from the back of the Jetstor unit - there were 3 of them.
4. Reconnected the power cords, turned the power switches back on to their "1" position.

After a couple of minutes, the front LCD display seemed to indicate that it had finished running some internal checks. The messages indicating failure of power units, which was previously constantly displayed on the front LCD panel, was no longer seen. Going back to the control room and checking the web diagnostics page, everything seemed back to normal.

However, FB still will not boot up. The error is identical to that discussed in this thread by Intel. It seems FB is having trouble finding its boot disk. I was under the impression that only the FE machines were diskless, and that FB had its own local boot disk - in which case I don't know why this error is showing up. According to the linked thread, it could also be a problem with the network card/cable, but I saw both lights on the network switch port FB is connected to turn green when I powered the machine on, so this seems unlikely. I tried following the steps listed in the linked thread but got nowhere, and I don't know enough about how FB is supposed to boot up, so I am leaving things in this state now.