title: Why my new Ceph cluster status never shows 'HEALTH_OK'?
body: <p>I'm working on setup a Ceph cluster with Docker and image 'ceph/daemon:v3.1.0-stable-3.1-luminous-centos-7'. But after the cluster has been setup, the <code>ceph status</code> command never reaches HEALTH_OK. Here is my cluster's information. It has enough disk space and the network is all right.</p>
  
  <p>My question are:</p>
  
  <ol>
  <li>Why does Ceph not replicate the 'undersized' pages?</li>
  <li>How to fix it?</li>
  </ol>
  
  <p>Thank you very much!</p>
  
  <pre><code>➜  ~ ceph -s
    cluster:
      id:     483a61c4-d3c7-424d-b96b-311d2c6eb69b
      health: HEALTH_WARN
              Degraded data redundancy: 3 pgs undersized
  
    services:
      mon:        3 daemons, quorum pc-10-10-0-13,pc-10-10-0-89,pc-10-10-0-160
      mgr:        pc-10-10-0-89(active), standbys: pc-10-10-0-13, pc-10-10-0-160
      mds:        cephfs-1/1/1 up  {0=pc-10-10-0-160=up:active}, 2 up:standby
      osd:        5 osds: 5 up, 5 in
      rbd-mirror: 3 daemons active
      rgw:        3 daemons active
  
    data:
      pools:   6 pools, 68 pgs
      objects: 212 objects, 5.27KiB
      usage:   5.02GiB used, 12.7TiB / 12.7TiB avail
      pgs:     65 active+clean
               3  active+undersized
  
  ➜  ~ ceph osd tree
  ID CLASS WEIGHT   TYPE NAME               STATUS REWEIGHT PRI-AFF
  -1       12.73497 root default
  -5        0.90959     host pc-10-10-0-13
   3   hdd  0.90959         osd.3               up  1.00000 1.00000
  -7        0.90959     host pc-10-10-0-160
   4   hdd  0.90959         osd.4               up  1.00000 1.00000
  -3       10.91579     host pc-10-10-0-89
   0   hdd  3.63860         osd.0               up  1.00000 1.00000
   1   hdd  3.63860         osd.1               up  1.00000 1.00000
   2   hdd  3.63860         osd.2               up  1.00000 1.00000
  ➜  ~ ceph osd pool ls detail
  pool 1 'cephfs_data' replicated size 3 min_size 2 crush_rule 0 object_hash rjenkins pg_num 8 pgp_num 8 last_change 24 flags hashpspool stripe_width 0 application cephfs
  pool 2 'cephfs_metadata' replicated size 3 min_size 2 crush_rule 0 object_hash rjenkins pg_num 8 pgp_num 8 last_change 24 flags hashpspool stripe_width 0 application cephfs
  pool 3 '.rgw.root' replicated size 3 min_size 2 crush_rule 0 object_hash rjenkins pg_num 13 pgp_num 13 last_change 27 flags hashpspool stripe_width 0 application rgw
  pool 4 'default.rgw.control' replicated size 3 min_size 2 crush_rule 0 object_hash rjenkins pg_num 13 pgp_num 13 last_change 30 flags hashpspool stripe_width 0 application rgw
  pool 5 'default.rgw.meta' replicated size 3 min_size 2 crush_rule 0 object_hash rjenkins pg_num 13 pgp_num 13 last_change 32 owner 18446744073709551615 flags hashpspool stripe_width 0 application rgw
  pool 6 'default.rgw.log' replicated size 3 min_size 2 crush_rule 0 object_hash rjenkins pg_num 13 pgp_num 13 last_change 34 flags hashpspool stripe_width 0 application rgw
  </code></pre>