I have a 5C bought a couple of months ago, running latest firmware (4.1.2) and dashboard (3.4.2) connected directly to a Mac mini (2018) running macOS Mojave 10.14.5 with the Drobo supplied USB cable.
I cannot essentially use the Drobo in any “sleep” configuration. It will disconnect on waking up the mini. Power Nap is disabled. And if you reboot the mini without first unmounting it and shutting it down, it will also disconnect several seconds/couple of minutes after rebooting macOS (if you are copying a file to it or from it, it will give an error and stop the operation). Once it disconnected after cold boot of both Mini and Drobo…
On a side note: My Mini also shows weird behaviour when using heavily the USB3 ports - the Apple original Magic Mouse on BT would lag when the USB3 ports are used (USB C ports don’t give me the same issue and the Magic Mouse works perfectly fine on an iMac late 2013 that also has USB3 ports, but of course in a completely different design/shielding). I ended up using a USB mouse…
So for me there is a fault both at Apple and Drobo. Support of USB3 from Apple doesn’t seem perfect at all, and Drobo is having issues in fixing what Apple seems to break or change constantly (like Wifi in the past years ).
I had a regular HDD in a cheap enclosure and it would go to sleep and wake up correctly on this Mini.
But the Drobo is a lot more complex machine, essentially a Linux box with a complex flexible RAID configuration, pretending to be a USB3 drive, and clearly there are message conflicts between the Drobo and the Mini/macOS, that have the Drobo behave weirdly.
BTW, when the Drobo goes to sleep, sometimes after 1 min it wakes up again and then after a few more seconds it sleeps again. Somehow the Mini sends a message that the Drobo recognises as “wake up” or the Drobo for some reason decides to wake up on its own, to do nothing…(no HDD activity heard).
So now I simply disabled all sleep functions on the Mini, as well as on the Drobo (disk spin down is off), and unmount it and turn it off at the end of the day. It works ok because it is not a work disk but more of a back up.
I think the Drobo hardware is ok, it is a plain software issue. If Apple or Drobo are at fault, hard to say.
I files with Drobo Support a ticket since the very beginning. They have been prompt in reply and it has been escalated (as per email from 2 days ago). The issue seems to be common enough to get attention and to take quite some time for them to figure out what is going on.
PS: I tried the Drobo 5C on an older MacBook Pro without the Drobo Dashboard software and same behaviour. So it seems the Drobo Dashboard software has no fault of its own. I don’t know how it behaves on a Windows machine as I don’t have one to try it on.
PS2: all my data is backed up in any case elsewhere (as it should be!!!) but so far no data loss.