Comment 2 for bug 1540376

The ceph charms do not currently support upgrading between releases using the config settings - this is a deploy time only option.

That said it would be a nice feature, but doing this via config alone is not a great idea as it will cause outages in the underlying storage cluster - so I would suggest that the existing config option is supplemented with an action to upgrade ceph on each unit as directed by the end user.