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<section id="best-practices-vm">
        <title>Best Practices for Virtual Machines</title>
        <para>For VMs to work as expected and provide excellent service, follow these guidelines.</para>
        <section id="best-practices-vm-monitoring">
                <title>Monitor VMs for Max Capacity</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>
        <section id="best-practices-vm-tools">
                <title>Install Required Tools and Drivers</title>
                <para>Be sure the following are installed on each VM:</para>
                <itemizedlist>
                        <listitem><para>For XenServer, install PV drivers and Xen tools on each VM.
                                This will enable live migration and clean guest shutdown.
                                Xen tools are required in order for dynamic CPU and RAM scaling to work.</para></listitem>
                        <listitem><para>For vSphere, install VMware Tools on each VM.
                                This will enable console view to work properly.
                                VMware Tools are required in order for dynamic CPU and RAM scaling to work.</para></listitem>
                </itemizedlist>
                <para>To be sure that Xen tools or VMware Tools is installed, use one of the following techniques:</para>
                <itemizedlist>
                        <listitem><para>Create each VM from a template that already has the tools installed; or,</para></listitem>
                        <listitem><para>When registering a new template, the administrator or user can indicate whether tools are
                                installed on the template. This can be done through the UI
                                or using the updateTemplate API; or,</para></listitem>
                        <listitem><para>If a user deploys a virtual machine with a template that does not have
                                Xen tools or VMware Tools, and later installs the tools on the VM,
                                then the user can inform &PRODUCT; using the updateVirtualMachine API.
                                After installing the tools and updating the virtual machine, stop
                                and start the VM.</para></listitem>
                </itemizedlist>           
        </section>
</section>