docs/en-US/about-secondary-storage.xml

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<section id="about-secondary-storage">
    <title>About Secondary Storage</title>
    <para>Secondary storage stores the following:</para>
    <itemizedlist>
        <listitem><para>Templates &mdash; OS images that can be used to boot VMs and can include additional configuration information, such as installed applications</para></listitem>
        <listitem><para>ISO images &mdash; disc images containing data or bootable media for operating systems</para></listitem>
        <listitem><para>Disk volume snapshots &mdash; saved copies of VM data which can be used for data recovery or to create new templates</para></listitem>
    </itemizedlist>
    <para>The items in secondary storage are available to all hosts in the scope of
        the secondary storage, which may be defined as per zone or per region.</para>
    <para>To make items in secondary storage available to all hosts throughout the cloud, you can
        add object storage in addition to the
        zone-based NFS Secondary Staging Store.
        It is not necessary to
        copy templates and snapshots from one zone to another, as would be required when using zone
        NFS alone. Everything is available everywhere.</para>
    <para>&PRODUCT; provides plugins that enable both
        OpenStack Object Storage (Swift, 
        <ulink url="http://swift.openstack.org">swift.openstack.org</ulink>)
        and Amazon Simple Storage Service (S3) object storage.
        When using one of these storage plugins, you configure Swift or S3 storage for
        the entire &PRODUCT;, then set up the NFS Secondary Staging Store for each zone. The NFS
        storage in each zone acts as a staging area through which all templates and other secondary
        storage data pass before being forwarded to Swoft or S3.
        The backing object storage acts as a cloud-wide
        resource, making templates and other data available to any zone in the cloud.</para>
</section>