6.5.1

Table Of Contents
When you create a VM-Host anity rule, its ability to function in relation to other rules is not checked. So it
is possible for you to create a rule that conicts with the other rules you are using. When two VM-Host
anity rules conict, the older one takes precedence and the newer rule is disabled. DRS only tries to satisfy
enabled rules and disabled rules are ignored.
DRS, vSphere HA, and vSphere DPM never take any action that results in the violation of required anity
rules (those where the virtual machine DRS group 'must run on' or 'must not run on' the host DRS group).
Accordingly, you should exercise caution when using this type of rule because of its potential to adversely
aect the functioning of the cluster. If improperly used, required VM-Host anity rules can fragment the
cluster and inhibit the proper functioning of DRS, vSphere HA, and vSphere DPM.
A number of cluster functions are not performed if doing so would violate a required anity rule.
n
DRS does not evacuate virtual machines to place a host in maintenance mode.
n
DRS does not place virtual machines for power-on or load balance virtual machines.
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vSphere HA does not perform failovers.
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vSphere DPM does not optimize power management by placing hosts into standby mode.
To avoid these situations, exercise caution when creating more than one required anity rule or consider
using VM-Host anity rules that are preferential only (those where the virtual machine DRS group 'should
run on' or 'should not run on' the host DRS group). Ensure that the number of hosts in the cluster with
which each virtual machine is aned is large enough that losing a host does not result in a lack of hosts on
which the virtual machine can run. Preferential rules can be violated to allow the proper functioning of DRS,
vSphere HA, and vSphere DPM.
N You can create an event-based alarm that is triggered when a virtual machine violates a VM-Host
anity rule. In the vSphere Web Client, add a new alarm for the virtual machine and select VM is violating
VM-Host  Rule as the event trigger. For more information about creating and editing alarms, see the
vSphere Monitoring and Performance documentation.
vSphere Resource Management
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