All bays flashing-red is the “too many drives have been remoevd, your Drobo is offline” state - essentially there are not enough drives present for Drobo to do anything.
If one of the bays is flashing-red, that means that drive has failed (or been flagged bad) and been removed from the disk pack. This drive can (and should) be removed and replaced.
If one bay is solid yellow or solid red, that means space is getting low (yellow) or critically low (red) and Drobo wants you to replace that drive with a larger drive. You can replace any smaller drive - it doesn’t have to be the one Drobo “recommends.”
So… After the 4+ days of data protection, what is the LED state?
After it finishes data protection, it goes to one red light and the rest green. Drobo dashboard reports the drobo is low on disk space, and to replace the drive indicated by the red light. Try to replace the drive with a larger drive, and the drobo complains I’ve removed too many drives. If I put the old drive back in, data protection will start over again and take about 4 days. I’ve gone through this cycle twice
Drobo support requested the logs, but perhaps I’ll wait another few days for data protection, and try replacing a different drive instead of the same one each time, if I don’t hear back from support.