So, I made a mistake of making one of my exchange DB's live on an ReFS drive. RR server is on 2012r2 which can't complete Mountability checks because it can't mount the filesystem!! So, can I in-place upgrade the server to 2016? I'm guessing I probably can. something like, stop/disable RR service... and maybe more services, then run upgrade OS?
edit; I WON'T go to Server 2019, and my Exchange is on Server 2016, so looks like I'm good to backup ReFS. (ReFS still not supported on 2019)