Ok, so here’s the deal. I have half a dozen Drobo 5C units, connected to many different Macs (iMac, iMac Pro, Mini), they serve as NAS and TimeMachine destinations. The two I bought for the iMac Pros would crash and reboot if you started a very large file copy to them. I formatted them and reflashed the firmware, reinstalled the operating systems, nothing could make them reliable. So I contacted Drobo, they were, as usual, zero help, denied any responsibility and closed all of my support cases unceremoniously and ignore any new ones I create. Fantastic, half a dozen boat anchors full of drives.
I ended up moving those two Drobos to a Mac Mini that was serving as a NAS server. This sort-of fixed it, but not entirely, they were more reliable, but a huge file transfer would still crash them. I chalked it up to: Drobo has a terrible USB3 driver, Apple changed their USB3 chip (maybe the brand new chipset in the iMac Pro?) or driver and the new one is buggy, or there was a deeper issue that nobody at Apple or Drobo seemed to want to acknowledge or want to talk to me about. I was getting nowhere.
Fast forward to this week. Drobo released a new dashboard/driver package, 3.4.2 (I was previously at 3.2.1 on Mac OS 10.11.6). It won’t let you install it unless you upgrade to Sierra 10.12. So I was forced to upgrade the Mini to at least Sierra. BINGO. This Mini started acting just like the other systems. Large file copies would crash the Drobo and/or USB driver/bus and the whole thing would go sideways.
So, tomorrow, I will be downgrading everything to 10.11.6 and seeing if the issue goes away. I’m posting this here because I have not found this issue covered anywhere on the net and am looking for help and/or hoping I can help others that may be in the same boat.