For the full details and images, please see my reddit post: https://www.reddit.com/r/drobo/comments/g58m2l/added_5th_drive_to_my_5d_now_nothing_seems_to/
To summarize, my Drobo 5D was running out of space so I purchased a WD 6TB RED drive to put into empty bay 4. The drive is listed as compatible on Drobos website.
Shortly after installing the drive, the Drobo went into a critical state.
After a lot of troubleshooting and research - it seems that WD secretly changed their RED drives to SMR, which has caused the issue with my Drobo. My Drobo’s Bay 0-3 are all 3TB WD RED drives.
I currently cannot access my Drobo 5D. I’ve removed the 6TB drive from bay 4, so it is empty again. All of the lights are red, with Bay 1 flashing red. I’m not sure the safest way to proceed.
Again, there are images and more detailed steps listed in the reddit post. Any help would be appriciated.