[ceph-users] cephfs slow, howto investigate and tune mds configuration?

Say I think my cephfs is slow when I rsync to it, slower than it used to be. First of all, I do not get why it reads so much data. I assume the file attributes need to come from the mds server, so the rsync backup should mostly cause writes not? I think it started being slow, after enabling snapshots on the file system. - how can I determine if mds_cache_memory_limit = 8000000000 is still correct? - how can I test the mds performance from the command line, so I can experiment with cpu power configurations, and see if this brings a significant change?