Why would my external USB3 drive (a Drobo) keep getting disconnected? I have a mac mini (Mid 2011) running High Sierra (10.13.4) that I've been trying to use a home server. I'm not sure what the cause is, but my external USB drive (a 3rd-gen 4-drive Drobo) keeps disconnected after 16-48 hours. The Drobo is out of warranty and since June 2017 Drobo doesn't provide any community support so I haven't been able to figure out if the issue originates with the device. Aside from power cycling (which isn't the cause in my case) what might cause a USB drive to disconnect ?
Are you using the USB cable that came with the Drobo? I know I got a bad one with my Drobo 5D that Drobo had to replace. I also recall some discussion a few years back about issues with Drobos sometimes disconnecting when the host went to sleep. Is your Mini set to never sleeps do not to sleep the connected drives?

I’m using a Thunderbolt connection with my 2012 Mini so my only USB/Drobo experience is a 5D with Windows 10.