If you create a DRS affinity rule for your cluster, you can specify how vSphere HA applies that rule during a virtual machine failover.
The two types of rules for which you can specify vSphere HA failover behavior are the following:
VM anti-affinity rules force specified virtual machines to remain apart during failover actions.
VM-Host affinity rules place specified virtual machines on a particular host or a member of a defined group of hosts during failover actions.
When you edit a DRS affinity rule, you must use vSphere HA advanced options to enforce the desired failover behavior for vSphere HA.
HA must respect VM anti-affinity rules during failover -- When the advanced option for VM anti-affinity rules is set, vSphere HA does not fail over a virtual machine if doing so violates a rule. Instead, vSphere HA issues an event reporting there are insufficient resources to perform the failover.
HA should respect VM to Host affinity rules during failover --vSphere HA attempts to place VMs with this rule on the specified hosts if at all possible.
For more information, see vSphere HA Advanced Options.
vSphere HA can restart a VM in a DRS-disabled cluster, overriding a VM-Host affinity rules mapping if the host failure happens soon (by default, within 5 minutes) after setting the rule.