Information Technology Reference
In-Depth Information
Figure 12.24
Use the buttons to
add or remove VMs
or hosts from a DRS
group. h is screen
shot shows VMs
added to a DRS
group.
The previous steps are the same for both VM DRS groups and host DRS groups, and you'll
need to have at least one of each group dei ned before you can create the rule.
After you've dei ned your VM DRS groups and host DRS groups, you're ready to actually
dei ne the host afi nity rule. The host afi nity rule brings together a VM DRS group and a host
DRS group along with the preferred rule behavior. There are four host afi nity rule behaviors:
Must Run On Hosts In Group
◆
◆
Should Run On Hosts In Group
Must Not Run On Hosts In Group
◆
Should Not Run On Hosts In Group
◆
These rules are, for the most part, self-explanatory. Each rule is either mandatory (“Must”)
or preferential (“Should”) plus afi nity (“Run On”) or anti-afi nity (“Not Run On”). Mandatory
host afi nity rules—those with “Must”—are honored not only by DRS but also by vSphere HA
and vSphere DPM. For example, vSphere HA will not perform a failover if the failover would
violate a required host afi nity rule. Preferred rules, on the other hand, might be violated.
Administrators have the option of creating an event-based alarm to monitor for the violation
of preferred host afi nity rules. You'll learn about alarms in Chapter 13, “Monitoring VMware
vSphere Performance.”
Figure 12.25 shows a host afi nity rule coming together with a selected VM DRS group, a rule
behavior, and a selected host DRS group.
Be careful when dei ning host afi nity rules, especially mandatory host afi nity rules like the
one shown in Figure 12.25, or you could run into a situation where VMs are severely limited on
where they can run; this is illustrated in Figure 12.26.
