Ceph - Crush Map has Legacy Tunables

I upgraded Ceph from the old Dumpling version to the latest Jewel version. In addition to the OSDs not able to start up due to some permission settings on /var/lib/ceph (we need to change the permission settings recursively to ceph:ceph), I am also having this HEALTH_WARN messages:

indra@sc-test-nfs-01:~$ ceph status
    cluster d3dc01a3-c38d-4a85-b040-3015455246e6
     health HEALTH_WARN
            too many PGs per OSD (512 > max 300)
            crush map has legacy tunables (require bobtail, min is firefly)
            crush map has straw_calc_version=0
     monmap e3: 3 mons at {sc-test-ceph-01=192.168.3.3:6789/0,sc-test-ceph-02=192.168.3.4:6789/0,sc-test-nfs-01=192.168.3.2:6789/0}
            election epoch 50, quorum 0,1,2 sc-test-nfs-01,sc-test-ceph-01,sc-test-ceph-02
     osdmap e100: 3 osds: 3 up, 3 in
      pgmap v965721: 704 pgs, 6 pools, 188 MB data, 59 objects
            61475 MB used, 1221 GB / 1350 GB avail
                 704 active+clean

To resolve the problem is very simple, use below command:

ceph osd crush tunables optimal

indra@sc-test-nfs-01:~$ ceph osd crush tunables optimal
adjusted tunables profile to optimal

Ceph status after the adjustment:

indra@sc-test-nfs-01:~$ ceph status
    cluster d3dc01a3-c38d-4a85-b040-3015455246e6
     health HEALTH_WARN
            too many PGs per OSD (512 > max 300)
     monmap e3: 3 mons at {sc-test-ceph-01=192.168.3.3:6789/0,sc-test-ceph-02=192.168.3.4:6789/0,sc-test-nfs-01=192.168.3.2:6789/0}
            election epoch 50, quorum 0,1,2 sc-test-nfs-01,sc-test-ceph-01,sc-test-ceph-02
     osdmap e101: 3 osds: 3 up, 3 in
      pgmap v965764: 704 pgs, 6 pools, 188 MB data, 59 objects
            61481 MB used, 1221 GB / 1350 GB avail
                 704 active+clean

The warning messages related to the crush map are gone. Yay!

PS. Ignore the "too many PGs per OSD" warning, due to I have limited number of OSDs and too many pools and PGs on my test environment.

Source: https://www.mail-archive.com/ceph-users@lists.ceph.com/msg10225.html
Reference: http://docs.ceph.com/docs/master/rados/operations/crush-map/