A disk failed on my Drobo 5N2. Happens.
When I migrated from a Drobo 5N to a 5N2 back in May I simply moved the HDDs over. This is the second Seagate desktop HDD to fail since January 2014. One 4TB, and one 3TB disk have failed – I am replacing the 3TB with a 4TB as they are cheap now. I use the Drobo for all my home music, movie and photo storage. It sees a lot of use.
Swapping a disk out takes about a minute if you include opening the packaging.