so we have 7 nodes set up to use ceph. I am starting to test ceph-fs does it make sense to have all nodes be a mds? or like mons limit it to 3 ? for 'hotstandby parameter option' - I assume all mds systems should use that option - if not please advise. thanks
Not really, the standby MDS need to sync with the primary MDS and as long as you don't see the MDS getting overloaded with client traffic, there is no need to put away the extra resources.