Upgrade from 4 to 5 drives and swap 2 out - how?

Hello, i currently have a Drobo S with 4 2TB Drives. Drives 1&2 are from manufacturer A and 3&4 are from B. I want to replace 3&4 with 3 new drives from A. How do i go about it? Do i first add the fifth drive and then swap out drive 3 and after Drobo S has returned to a save state then swap out 4 or do i first swap an then add the fifth drive? DualDisk Redundancy is enabled.

You can add drives at any time.
However, you can only remove drives when Drobo is ready - or you risk losing data.

It is important not to remove any drives while Drobo is blinking green-yellow/orange.

Since you have an empty bay, I would first add the new drive from A into the empty slot. This helps to avoid degrading from DDR to SDR during the next steps, unless your new drives are smaller than the ones you’re replacing.

Replace drive 3 with new drive from A
Wait for relayout to complete
Replace drive 4 with new drive from A
Wait for relayout to complete (or at this point you can go about normal business, just remember that Drobo will be significantly slower until the relayout is completed).

Great, thanks. I added the fifth drive and an then swapped #3 for a new one. Dashboard says about 12h for relayout to complete.