Frank Denneman, Senior Technical Marketing Architect, VMware
vSphere 4.1 and vSphere 5 offer the ability to create virtual machine to host affinity rules. A VM-Host affinity rule specifies an affinity relationship between a group of virtual machines and a group of hosts. There are 'mandatory' rules (designated by "must") and 'preferential' rules (designated by "should".)
DRS will honor preferential rules during load-balancing operations and Host maintenance mode operations. Mandatory rules apply to non-DRS operations even in a DRS cluster, such as manual power-on operations, manual vMotions or VMware HA host failover events.
The intended use case for mandatory rules is ISV licensing compliance. This use case is considered important enough to leave the rules active even after DRS is not available, such as a vCenter outage or when DRS is disabled. Therefore disabling DRS will not indirectly remove the mandatory rules.
Before disabling DRS, remove mandatory rules first. After disabling DRS, the vSphere client does not continue to show the rules tab for the affinity rules. You will need to re-enable DRS, remove the rules and then disable DRS.
