Quick tip to enable the dynamic subtree tree partitionning with multiple Ceph MDS servers.
If you want this to take effect during cluster creation edit your ceph.conf:
[mds]
mds max = 5
Then restart your MDSs, they will be all active.
Or inject the following command:
$ ceph mds set_max_mds 5
max_mds = 5
Before and after:
$ ceph -s
cluster 04c9ddfb-a420-4fac-bbee-997fd182f527
health HEALTH_OK
monmap e1: 1 mons at {ceph001=192.168.0.100:6789/0}, election epoch 1, quorum 0 ceph001
mdsmap e20: 1/1/1 up {0=ceph006=up:active}, 4 up:standby
osdmap e103: 29 osds: 29 up, 29 in
pgmap v18261: 1216 pgs, 4 pools, 2145 bytes data, 23 objects
1237 MB used, 26771 GB / 26773 GB avail
6 active+clean+replay
1210 active+clean
$ ceph -s
cluster 04c9ddfb-a420-4fac-bbee-997fd182f527
health HEALTH_OK
monmap e1: 1 mons at {ceph001=192.168.0.100:6789/0}, election epoch 1, quorum 0 ceph001
mdsmap e30: 5/5/5 up {0=ceph006=up:active,1=ceph005=up:active,2=ceph003=up:active,3=ceph002=up:active,4=ceph004=up:active}
osdmap e103: 29 osds: 29 up, 29 in
pgmap v18274: 1216 pgs, 4 pools, 5893 bytes data, 85 objects
1239 MB used, 26771 GB / 26773 GB avail
1216 active+clean
Now enable the subtree partitionning with the following flag:
[mds]
mds bal frag = true
For all the options.