How-to quickly deploy a MDS server.
Assuming that /var/lib/ceph/mds/mds.$id is the mds data point.
Edit ceph.conf and add a MDS section like so: [mds.$id] host = {hostname}
Create the authentication key (only if you use cephX):
$ sudo ceph auth get-or-create mds.$id mon 'profile mds' mgr 'profile mds' mds 'allow *' osd 'allow *' > /var/lib/ceph/mds/ceph-$id/keying
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Eventually start the service:
$ sudo service ceph start mds.$id
=== mds.$id ===
Starting Ceph mds.$id on ceph...
starting mds.$id at :/0
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Check the status of the cluster:
$ ceph -s
cluster:
id: 109d9955-2d85-4222-a29f-77a25ec492b3
health HEALTH_OK
services:
mon: 3 daemons, quorum a,b,c
mgr: x(active)
mds: cephfs_a-1/1/1 up {0=c=up:active}, 3 up:standby
osd: 3 osds: 3 up, 3 in
data:
pools: 2 pools, 16 pgs
objects: 22 objects, 2.2 KiB
usage: 3.2 GiB used, 27 GiB / 30 GiB avail
pgs: 16 active+clean
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Note if you want to add more MDSs, they will appear like this:
$ ceph -s
cluster:
id: 109d9955-2d85-4222-a29f-77a25ec492b3
health HEALTH_OK
services:
mon: 3 daemons, quorum a,b,c
mgr: x(active)
mds: cephfs_a-1/1/1 up {0=c=up:active}, 4 up:standby
osd: 3 osds: 3 up, 3 in
data:
pools: 2 pools, 16 pgs
objects: 22 objects, 2.2 KiB
usage: 3.2 GiB used, 27 GiB / 30 GiB avail
pgs: 16 active+clean
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Easy, isn’t it? The filesystem metadata live in RADOS cluster. So MDS servers are quite ephemeral daemons. Don’t be surprised if you don’t find anything (expect the MDS key) inside the mds data directory.