It's very handy to be able to quickly glance at a dashboard and see how many OSDs are Up and In. The following two queries show these values:

maxSeries(collectd.mon*.ceph.mon.mon*.ceph_bytes.Cluster.numOsdIn)

maxSeries(collectd.mon*.ceph.mon.mon*.ceph_bytes.Cluster.numOsdUp)

Note the use of the maxSeries function, which allows data to be pulled from all the mon nodes and will take the highest value.