Wednesday, April 11, 2012

When you cant afford host based HA failover and use % based HA failover

Issue - when trying to put the host in maintenance mode the VMs are not being moved automatically for a cluster.
Only few VMs migrated off of the host.
Action - It was a 2 node cluster.
50% of the resources have been reserved for HA failover that means 1 out of 2 hosts is reserved for HA failover.
When 1 of the 2 hosts is put into maintenance mode the HA cannot satisfy its rule of reserving 50% of the resources of the cluster where only one host is powered on and further more the admission control for the HA is enabled which stops the VMs from being powered on which violate the resource availability.
Disabling the admission control and disabling HA moved the VMs automatically to another host when one of the host was put into the maintenance mode.
Recommendation: In a 2 node cluster never enable the admission control for HA especially if we are using the % based HA failover instead of host based failover.
In a cluster with more than 3 hosts it is advisable to use the host based HA failover but not % based failover. Wherever % based failover is used for the lack of resources to use the host based HA failover admission control should be disabled if you want all of your VMs to be powered on irrespective of the availability of resources.