I have a new Onyx350 that has two identical hard drives. The drives
function fine however, I get not activity on the either of the drive's LED.
The LED is actually lit up by the bus backplane that the drives plug into.
Is there a switch somewhere either in hardware or software to turn those
lights on? I'm running Irix 6.5.21.

I have several other Onyx350s that do show activity on the hard drive LEDs
but I haven't found any setting differences between the two machines.