Adding a new drive problem maybe?

I have a 2nd gen Drobo that had 4 3TB WD Green drives that was working well. Then I read that those drives were incompatible so I decided I would change them out with compatible drives and upgrade the drives to 4 TB, the max for this device as I understand.

I put in one new drive and it behaved normally. I understood I could continue to use the drive, which I did without incident. After 24 hours the lights are still blinking so I decided maybe my using the drive was slowing the transformation so I stopped using it. After about 48 hours I noticed the device had disappeared from the finder and the Drobo Dashboard although it still appeared to be working to adapt to the new drive (the blue lights are still across the bottom and it is blinking green and red).

It is now 4 days and everything is still blinking and I occasionally hear the fans and drives working but this is still going on. When should I start worrying? What happens if a power failure occurs while this is occurring?

Your old WD greens probably pre-date WD switching to SMR when making them, if so they’re actually perfectly OK, something you can probably research by serial numbers etc. if you wish.

Rebuilds on Gen 2 devices are slow, they can sometimes take as long as 24 hrs per TB of data or even longer if also being used, last time I fed my old Gen 2 a 4TB drive to replace something smaller the rebuild took over a week, with it appearing & disappearing from dashboard a number of times while remaining available in explorer (Windows user here).

A sudden power loss may cause issues, if you live somewhere power losses & or glitches are common it’s a very good idea to run Drobos (or other similar storage devices) via a UPS.

Indeed, the rebuild was slow. Finally complete after a week. What really bothered me was it disappearing from the finder/Drobo Dashboard.