docs/en-US/best-practices-for-vms.xml

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<section id="best-practices-vm">
	<title>Best Practices for Virtual Machines</title>
	<para>The &PRODUCT; administrator should monitor the total number of VM instances in each
        cluster, and disable allocation to the cluster if the total is approaching the maximum that
        the hypervisor can handle. Be sure to leave a safety margin to allow for the possibility of
        one or more hosts failing, which would increase the VM load on the other hosts as the VMs
        are automatically redeployed. Consult the documentation for your chosen hypervisor to find
        the maximum permitted number of VMs per host, then use &PRODUCT; global configuration
        settings to set this as the default limit. Monitor the VM activity in each cluster at all
        times. Keep the total number of VMs below a safe level that allows for the occasional host
        failure. For example, if there are N hosts in the cluster, and you want to allow for one
        host in the cluster to be down at any given time, the total number of VM instances you can
        permit in the cluster is at most (N-1) * (per-host-limit). Once a cluster reaches this
        number of VMs, use the &PRODUCT; UI to disable allocation of more VMs to the
        cluster.</para>
</section>