Which is a valid reason NOT to set CPU affinity on a single VM?
A.
Setting CPU affinity will monopolize a CPU making it unusable for other VMs on the server.
B.
CPU affinity can only be set on hyperthreaded systems.
C.
A virtual machine with CPU affinity might not receive all of it’s reserved CPU resources.
D.
CPU affinity settings are ignored when using VMotion.
Explanation:
Potential Issues with CPU Affinity
Before you use CPU affinity, you might need to consider certain issues.
Potential issues with CPU affinity include:
Affinity can interfere with the ESX/ESXi host’s ability to meet the reservation and shares specified for a virtual machine.
Answer should be D: CPU affinity settings are ignored when using vmotion
Answer C : is applicable only when using manual affinity rule . otherwise it is not adversely affected . but when u move a VM from one host to anoher(which is vmotion) the afinity is lost .
■ Affinity can interfere with the ESXi host’s ability to meet the reservation and shares specified for a virtual machine.
■ Because CPU admission control does not consider affinity, a virtual machine with manual affinity settings might not always receive its full reservation.
Virtual machines that do not have manual affinity settings are not adversely affected by virtual machines with manual affinity settings.
■ When you move a virtual machine from one host to another, affinity might no longer apply because the new host might have a different number of processors.
According to “Mastering VMware vSphere 5”, “The VM must not have it’s CPU affinity set to a specific CPU”.
Strange that he should put it that way. Earlier in the book he defines CPU affinity as:
“…to statically associate a VM to a specific physical CPU core.”
The he says:
“CPU affinity breaks vMotion”.
It seems that ‘C’ is correct.