Comment 1 for bug 1782245

"A value of 0 will cause the charm to only consider the actual number of OSDs in the cluster."

If you have that many OSD's you really do need to set the expected-osd-count; the PG calc will happen early in the deployment based on the number of in OSD's at that point in time, which will be inaccurate and then the OSD's join, the PG's spread and the number per OSD drops well below the target of 100/200/300.