Here are some numbers of when I tried increasing the number of OSDs in a deployment I had:
WIth 3 OSDs: health HEALTH_WARN too many PGs per OSD (865 > max 300)
With 6 OSDs (I added 3 nodes to the existing deployment): health HEALTH_WARN too many PGs per OSD (432 > max 300)
Here are some numbers of when I tried increasing the number of OSDs in a deployment I had:
WIth 3 OSDs:
health HEALTH_WARN
too many PGs per OSD (865 > max 300)
With 6 OSDs (I added 3 nodes to the existing deployment):
health HEALTH_WARN
too many PGs per OSD (432 > max 300)