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A host in a 4-node HADRS cluster has failed. HA initiates restart tasks for the virtual machines on the remaining hosts in the cluster but half of them fail to restart.
What is the likely reason virtual machines fail to restart?
A. HA admission control is blocking the restart of the virtual machines due to insufficient resources to support the configured failover level of the cluster.
B. The vMotion network has failed on the remaining hosts preventing the virtual machines from migrating.
C. Storage vMotion has failed on the datastore containing the virtual machines preventing them from migrating.
D. The failed host was the Master host in the cluster and no other hosts are able to perform the necessary HA function to restart the virtual machines.
Correct Answer: A
Explanation/Reference:
Explanation:
In this question, Admission Control is incorrectly configured. That is, it is not configured for HA. If the HA type of admission control is not enabled, then the VMs will not restart if there are insufficient resources. With the HA type of admission control enabled, the required resources would be reserved and the VMs would be able to start. vCenter Server uses admission control to ensure that sufficient resources are available in a cluster to provide failover protection and to ensure that virtual machine resource reservations are respected.
Three types of admission control are available.
Host: Ensures that a host has sufficient resources to satisfy the reservations of all virtual machines running on it.
Resource Pool: Ensures that a resource pool has sufficient resources to satisfy the reservations, shares, and limits of all virtual machines associated with it. vSphere HA: Ensures that sufficient resources in the cluster are reserved for virtual machine recovery in the event of host failure.
Admission control imposes constraints on resource usage and any action that would violate these constraints is not permitted. Examples of actions that could be disallowed include the following:
Powering on a virtual machine.
Migrating a virtual machine onto a host or into a cluster or resource pool.
Increasing the CPU or memory reservation of a virtual machine.
Of the three types of admission control, only vSphere HA admission control can be disabled. However, without it there is no assurance that the expected number of virtual machines can be restarted after a failure.
Incorrect Answers:
B: vMotion is not used in an HA failover. The VMs are not vMotioned from the failed host to another host; they are just restarted on another host. Therefore, this answer is incorrect.
C: Storage vMotion is not used in an HA failover. The VMs are not moved to another datastore; they remain in place on their current datastore on shared storage. Therefore, this answer is incorrect.
D: Other hosts are able to perform the necessary HA function to restart the virtual machines in the event of a failure of ANY host in the HA cluster. Therefore, this answer is incorrect.
References:
http://pubs.vmware.com/vsphere-55/index.jsp#com.vmware.vsphere.avail.doc/GUID-53F6938C-96E5-4F67-9A6E-479F5A894571.html
