CephBasics

Check Ceph cluster status

The command :

ceph -s

shows the actual status of the Ceph cluster :

[root@cephq1 ~]# ceph -s
    cluster 82766e04-585b-49a6-a0ac-c13d9ffd0a7d
     health HEALTH_OK
     monmap e1: 3 mons at {cephq2=192.168.41.2:6789/0,cephq3=192.168.41.3:6789/0,cephq4=192.168.41.4:6789/0}
            election epoch 8, quorum 0,1,2 cephq2,cephq3,cephq4
     osdmap e78: 6 osds: 6 up, 6 in
      pgmap v1293: 192 pgs, 2 pools, 0 bytes data, 0 objects
            27920 kB used, 4021 GB / 4106 GB avail
                 192 active+clean

The following command displays a real-time summary of the status of the cluster, and major events :

ceph -w

Remove OSDs

When you want to remove a machine that contains OSDs (for example : decommissioning of an old equipment out of warranty), there is manual procedure to follow in order to do things in a clean way and to avoid problems :

1. Identify the OSDs hosted by the machine with the command :

ceph osd tree

1. Take the OSDs out of the cluster :

Before you remove an OSD, it is usually up and in. You need to take it out of the cluster so that Ceph can begin rebalancing and copying its data to other OSDs :

ceph osd out {osd-num}

Repeat this operation for all the OSDs on the machine.