Negative values are being reported for IOPS in the "system servers" dashboard
This was a dockerized environment. Negative rate values were seen because read/write counters were dropping below the previous values at random times. On further investigation, it revealed that this was due to the docker volume groups present on the host. It is expected of docker containers to add/remove the volume groups during the lifecyle of a container. So, when a volume group goes away, the read/write counters do not contribute to the total counter values, thus making the value go below the last seen value.
Have a provision to discard such "special" disk partitions through a skip pattern. Individual disk counter metrics can be used to get disk specific counter values. If skipped, they will not contribute to the global counter metric.