--On Friday, September 18, 2020 10:53 PM +0200 Simon Matter <simon.matter at invoca.ch> wrote: > mdadm --remove /dev/md127 /dev/sdf1 > > and then the same with --add should hotremove and add dev device again. > > If it rebuilds fine it may again work for a long time. This worked like a charm. When I added it back, it told me it was "re-adding" the drive, so it recognized the drive I'd just removed. I checked /proc/mdstat and it showed rebuilding. It took about 90 minutes to finish and is now running fine.