Trying to troubleshoot one problem, I encountered a worse one.
I tried running the Volume Structure scan in the latest Tech Tool Pro 5 on a nearly-empty 2Tb partition on a full-up 8-Tb 1st-gen Drobo. The first thing the scan does is a quick look at the overall volume structure. Things became odd right away. Tech Tool Pro 5 displays an elapsed-time counter. This counter didn’t advance. After about five minutes, the scan reported failure (lack of response) and all three Drobo volumes were dismounted. Drobo Dashboard reported no Drobo present, though it was still plugged in and the lights were on (all green).
This smelled funny so I tried again. This time, while the initial scan was going on, I used the Finder to browse the directory structure on the other two mounted volumes, to keep traffic flowing to and from the Drobo. The elapsed-time counter shown by Tech Tool Pro updated in fits and starts, but the first stage of the Volume Structure scan eventually completed. After that, the elapsed-time counter ticked off the seconds normally and the Volume Structure scan ran to completion with no further problems.
At a guess, the Drobo emulation is not servicing one kind of request queue, which is then overflowing, overwriting memory and crashing the Drobo. This is tickled by Tech Tool Pro 5, which obviously makes file system requests of a unique kind in a unique pattern. As long as the Drobo is kept busy satisfying other requests, it will clear out the offending queue by polling while working through the other queues.
Apple’s own Disk Utility doesn’t trigger this bug. One could argue that Tech Tool Pro 5 is the offender here, but a) that would be arguing in advance of the facts, and b) it shouldn’t be possible to crash a Drobo this way, no matter what.