I think 1 of 4 drives failed, but the drobo disk is no longer mountable

I have an old 4 bay Drobo 2. It has four 2TB drives in it and has around 45% capacity used.

The lights started flashing the other day - and unfortunately I don’t recall the exact sequence of events, but it wound up where one light was red and the others were either orange or green (or flashing between them).

So I ejected the drive with the red light and ordered a new drive.

After I ejected the drive, the other three drive lights flashed orange and green and have been doing so for almost a week. I thought this meant that the data was being rebuilt. I know it can take a long time for it to finish, so I’m not panicking yet…

My Mac see’s the drive in the system profiler on the USB tree, but the volume isn’t mounting. I tried rebooting the Mac, but the situation doesn’t change.

The new 2TB drive arrived today so I installed it in the empty slot, however the lights did not change. The three drives are still flashing orange and green and there is no light next to the new drive.

Does any of this sound normal? Should I do anything besides keep waiting?

I’ve recently been through exactly this with my Drobo Gen 2 (3 weeks flashing). It transpired that there was nothing wrong with the solid red drive, but this wasn’t established until I had wiped and reformatted all drives. Unfortunately I think it’s time for you to panic. Fortunately in my case I had it all backed up to Backblaze so I’ve lost nothing. Offsite backup is essential.