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High Availability Storage for High Availability Cluster
The Ceph cluster creates a default user named admin for cluster management during the cluster creation process. The user admin uses ceph.client.admin.keyring for all administrative tasks in a Ceph cluster.
Let's check our progress so far using the keys we just gathered. Simply run the following command to check the cluster status:
If all went ok this far, the previous command should print the following result on the screen:
cephadmin@ceph-mon-01:-/pmxceph$ sudo ceph -s cluster 472cefbe-11a6-40f7-a352-5d245ae89fb3 health HEALTH_ERR 192 pgs stuck inactive; 192 pgs stuck unclean; no osds monmap e2: 3 mons at {ceph-mon-01-192.168.10.11:6789/0, ceph-mon- 02-192.168.10.12:6789/0, ceph-mon-03-192.168.10.13:6789/0}, election epoch 6, quorum 0,1,2 ceph-mon-01, ceph-mon-02, ceph- mon-03 osdmap el: 0 osds: 0 up, 0 in pgmap v2: 192 pgs, 3 pools, 0 bytes data, 0 objects
0 kB used, 0 kB 0 kB avail
According to this status, we have successfully created our MONs. By default, Ceph creates three pools with 192 PGs. PGs are in creating mode because we have not added any OSD yet.
With the initial cluster and MONS setup, we are now ready to start adding OSDs in the Ceph cluster. For simplicity, we are going to put Journal on the same OSD. Without journaling, an OSD cannot function. Any data coming to the Ceph cluster is first written into the journal device and then transferred to OSD. Thus, performance can be increased greatly by putting Journal on SSD while using HDD for OSD.
For a small Ceph cluster, putting Journal on SSD is acceptable. When the cluster grows beyond eight OSDs per physical node, it is wise to put Journal on the same HDD. A lost journal due to SSD failure will cause mass data loss for any OSD that stores its journal on that SSD. By putting Journal on the same HDD, we prevent the single point of failure. To see the difference in performance for OSSD on SSD and HDD, see the section Ceph benchmarking section later in this chapter.