Hi @cjcenizal
Those links help in fixing it. This is exactly what I tried:
I have refreshed the metricbeat fields and I could see the diskio fields are searchable and aggregatable now.
I have also learned some useful GET queries which can tell us if the fields are mapped and are searchable and aggregatable or not.
GET metricbeat*/_mapping/metricsets/field/system.diskio.read.count
and
GET /_field_stats?fields=system.diskio.read.count