Here’s an interesting data point. I have two Drobo S units. On one of them, both Firewire 800 ports became unresponsive: plugging it into either of the two Macs I have with FW 800 wouldn’t wake up the unit, but USB or eSATA would. (One of the Macs has no eSATA ports, hence the keen interest in getting FW 800 working.)
I used the power switch to power the unit down, then pulled the power connector out of the chassis for about thirty seconds. This cure has been known to be necessary to get certain balky Mac Firewire controllers to unstick themselves, so I figured it was worth a try.
Rather to my surprise, it worked. FW 800 now works perfectly on that unit. So apparently the FW controllers used by Drobo Inc. in their Drobo S units (at least) are susceptible to the same malaise as some (generally older) Macs, and can be cured by the same method.
Thought I’d document this in the forums.