Editing Ceph Storage Cluster (section)

=== Single Host Operation ===
OOTB, ceph required replication to be across hosts, not just devices.  For a single node cluster (or small clusters with unbalanced disks), this can be problematic.  The following steps will add a new rule that will allow replication across OSDs instead of hosts:

 #
 # commands to set ceph to handle replication on one node
 #
 # create new crush rule allowing OSD-level replication
 # ceph osd crush rule create-replicated <rulename> <root> <level>
 ceph osd crush rule create-replicated osd_replication default osd
 
 # verify that rule exists and is correct
 ceph osd crush rule ls

 # get the id of the new rule (probably will be '1', but check anyway
 ceph osd crush rule dump
 
 # set replication level on existing pools
 ceph osd pool set device_health_metrics size 3 
 
 # apply new rule to existing pools
 ceph osd pool set device_health_metrics crush_rule osd_replication

 # make the new rule the default
 # ceph config set global osd_pool_default_crush_rule <rule_id>
 ceph config set global osd_pool_default_crush_rule 1