I am using a Mac Pro with High Sierra, I have had the Drobo second generation for many years and bought it back when it was new. After a particularly bad High Sierra security update, when I plugged my drobo back in, all lights were red with one flashing red light, the top one. I looked up “what the lights mean” and thought what I was seeing was because one drive had gone out…all the other lights were red telling me that I had to replace the blinking one.
I replaced the blinking one while the drive was turned on. Maybe this is where I screwed up. I don’t know. Now all the lights are a solid red. My thinking is that one of the drives was damaged when while moving my late 2013 Mac Pro around, it caused a small piece of hardware to fall next to it and the vibration could have damaged it.
Update: I removed the new empty 4 TB drive from the top bay, replaced the old drive in it’s place and after it turned on, it showed 3 green lights and a fourth that is red. The red one is on the bottom. The drive “sounds active” right now so I am very careful in replacing it. I’m not even sure if the drive is bad, but rather, is simply over capacity.
The truth is that one virtual drive has been yellow for awhile and of the 4.4 TB capacity there is only 184 GB left.