Information Technology Reference
In-Depth Information
Recall from the previous section that DRS rules are the second of two conditions that will
trigger a priority 1 recommendation (the other is maintenance mode). When DRS detects that
VMs will violate DRS rules, it generates a priority 1 recommendation to migrate one or more
VMs in order to satisfy the constraint expressed in the DRS rule.
vSphere's DRS rule functionality gives vSphere administrators the power to model the com-
plex relationships that often exist in today's datacenters. Let's take a closer look at each of these
three types of DRS rules.
Creating VM Affinity Rules
Afi nity rules keep VMs together on the same host. Consider a multitier application where you
have a web application server and a backend database server that frequently communicate with
each other and you'd like that communication to take advantage of the high-speed bus within
a single server rather than going across the network. In that case, you could dei ne an afi nity
rule (Keep Virtual Machines Together) that would ensure that these two VMs stay together in
the cluster.
Perform the following steps to create a DRS afi nity rule:
1.
Launch the Web Client if it is not already running, and connect to a vCenter Server
instance.
DRS and DRS rules cannot be managed when connected to a specii c ESXi host; you must
connect to a vCenter Server instance.
2.
Navigate to the Hosts And Clusters view.
3.
Right-click the DRS cluster where the rules need to exist, and select the Settings option.
4.
Click the DRS Rules option.
5.
Click the Add button near the top of the pane.
6.
Type a name for the rule, and select Keep Virtual Machines Together for the type of rule
to create.
7.
Click the Add button to include the necessary VMs in the rule. Simply select the check
box for the VMs you want to include in the DRS rule.
8.
Click OK.
9.
Review the new rule coni guration to ensure that it is correct.
10.
Click OK.
VM afi nity rules let you specify VMs that should always stay together, but what about VMs
that should always stay separate? DRS offers that functionality with VM anti-afi nity rules.
Creating VM Anti-Affinity Rules
Consider an environment with two mail server VMs. In all likelihood, administrators would not
want both mail servers to reside on the same ESXi host. Instead, the administrators would want
the mail servers split onto two different ESXi hosts in the cluster, so that the failure of one host
would affect only one of the two mail servers. In this sort of situation, a VM anti-afi nity rule is
the right tool to use.
