Thanks for your answer.
Is there's a conf file somewhere this information is written ? So far I have:
mtab:/dev/sdf1 /var/lib/ceph/osd/ceph-0 xfs rw,noatime,attr2,inode64,noquota 0 0
Which is not in the fstab or any conf file. So I guess it is kind of discovered by a process started as a...