When you have created a cluster and enable HA the default percentage for the Performance degradation VMs tolerate is 100%. I think this is a bit weird because why do you want to disable a warning when there is insufficient failover capacity to guarantee the same performance after VMs restart on the remaining hosts in the cluster.
When you are using too many resources and the utilization of your VM’s doesn’t fit on the remaining hosts in the cluster after a host failure wouldn’t you like to know it?
When you put this value on 0% this message appears: Running VMs utilization cannot satisfy the configured failover resources on the cluster Production in Datacenter.
Percentage of performance degradation the VMs in the cluster are allowed to tolerate during a failure. 0% – Raises a warning if there is insufficient failover capacity to guarantee the same performance after VMs restart. 100% – Warning is disabled.
If you leave this value on the default 100% and your virtual machines are not configured with reservations, admission control based on percentage doesn’t work. Only the virtual machine overhead is counted.
You can clearly see in the above screenshot that we have 97% of our cluster resources available for both memory and CPU while at the same time we received a warning that we’re running out over failover resources. So admission control based on percentage only works when VM’s are configured with reservations.