I played around with both LibreNMS and Observium and when having around 100-120 switches none of them was able to keep up with updating mysql and the RRD files.. When I looked into to the config file there was variable that pointed out where to find the RRD files so I simply changed the variable to point to another disk.. And now it works..
But to get even better performance I installed RRDcached (that is supporter by both) and when using ATOP command I can see that polling time have gone down substantially.
I will try to mount a disk under rrd-directory and see what the result is,, it should work, I think,, what doesnt work is sym-links, RRD dont like that
I will also try PHP devtools, iftools and nodetools and se if I can integrate with librenms/observium
About Grafana, Grafana have a Mysql and PostGress connector.
I will come back about my tests