We switched the default replica size for Ceph from 1 to 3 which is a better value for production environments (see BZ #1404459) but test and POC deployments with less than 3 OSDs will fail as Ceph pools are not usable (not accepting writes).

We should add into documentation a comment about the usage of:

parameter_defaults:
  CephPoolDefaultSize: 1

in the various examples related to Ceph, to make sure readers are aware of the param.

NOTE: it is possible to change the replica size for a pre-existing pool after the deployment is completed and such a change is effective immediately (bringing the cluster back in working state), I am documenting it here hoping it can be helpful but I don't think we should document these bits. For example, to change the size of the "images" pool:

# ceph osd pool set images size=1