My cluster was throwing warning Legacy BlueStore stats reporting detected and we could just not abide that.
Here's a simple way to upgrade:
cd /var/lib/ceph/osd
ls # note your osd numbers
ceph osd set noout
for n in 7 8 9 10 11 12 ; do
systemctl stop ceph-osd@$n.service;
ceph-bluestore-tool repair --path ceph-$n;
systemctl start ceph-osd@$n.service;
systemctl status ceph-osd@$n.service;
done
# I like to wait until the cluster goes back to green
# before doing the same on the next host
ceph osd unset noout