148 lines
7.9 KiB
XML
148 lines
7.9 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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version="5.0"
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xml:id="multi_backend">
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<title>Configure multiple-storage back ends</title>
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<para>When you configure multiple-storage back ends, you can
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create several back-end storage solutions that serve the same
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OpenStack Compute configuration and one <systemitem class="service">cinder-volume</systemitem>
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is launched for each back-end storage or back-end storage pool.</para>
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<para>In a multiple-storage back end configuration, each back end has a name
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(<literal>volume_backend_name</literal>). Several back
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ends can have the same name. In that case, the scheduler
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properly decides which back end the volume has to be created
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in.</para>
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<para>The name of the back end is declared as an
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extra-specification of a volume type (such as,
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<literal>volume_backend_name=LVM_iSCSI</literal>). When a
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volume is created, the scheduler chooses an appropriate back
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end to handle the request, according to the volume type
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specified by the user.</para>
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<simplesect>
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<title>Enable multiple-storage back ends</title>
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<para>To enable a multiple-storage back ends, you must set
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the <option>enabled_backends</option> flag in the
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<filename>cinder.conf</filename> file. This flag
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defines the names (separated by a comma) of the
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configuration groups for the different back ends: one name
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is associated to one configuration group for a back end
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(such as, <literal>[lvmdriver-1]</literal>).</para>
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<note>
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<para>The configuration group name is not related to the
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<literal>volume_backend_name</literal>.</para>
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</note>
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<para>The options for a configuration group must be defined in
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the group (or default options are used). All the standard
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Block Storage configuration options
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(<literal>volume_group</literal>,
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<literal>volume_driver</literal>, and so on) might be
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used in a configuration group. Configuration values in the
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<literal>[DEFAULT]</literal> configuration group are
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not used.</para>
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<para>These examples show three back ends:</para>
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<programlisting language="ini">enabled_backends=lvmdriver-1,lvmdriver-2,lvmdriver-3
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[lvmdriver-1]
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volume_group=cinder-volumes-1
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volume_driver=cinder.volume.drivers.lvm.LVMISCSIDriver
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volume_backend_name=LVM_iSCSI
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[lvmdriver-2]
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volume_group=cinder-volumes-2
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volume_driver=cinder.volume.drivers.lvm.LVMISCSIDriver
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volume_backend_name=LVM_iSCSI
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[lvmdriver-3]
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volume_group=cinder-volumes-3
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volume_driver=cinder.volume.drivers.lvm.LVMISCSIDriver
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volume_backend_name=LVM_iSCSI_b</programlisting>
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<para>In this configuration, <literal>lvmdriver-1</literal>
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and <literal>lvmdriver-2</literal> have the same
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<literal>volume_backend_name</literal>. If a volume
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creation requests the <literal>LVM_iSCSI</literal> back
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end name, the scheduler uses the capacity filter scheduler
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to choose the most suitable driver, which is either
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<literal>lvmdriver-1</literal> or
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<literal>lvmdriver-2</literal>. The capacity filter
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scheduler is enabled by default. The next section provides
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more information. In addition, this example presents a
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<literal>lvmdriver-3</literal> back end.</para>
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</simplesect>
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<simplesect>
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<title>Configure Block Storage scheduler multi back
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end</title>
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<para>You must enable the <option>filter_scheduler</option>
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option to use multiple-storage back ends. The filter scheduler:</para>
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<orderedlist>
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<listitem>
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<para>Filters the available back
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ends. By default,
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<literal>AvailabilityZoneFilter</literal>,
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<literal>CapacityFilter</literal> and
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<literal>CapabilitiesFilter</literal> are
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enabled.</para>
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</listitem>
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<listitem>
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<para>Weights the previously
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filtered back ends. By default, the
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<option>CapacityWeigher</option> option is
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enabled. When this option is enabled, the filter
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scheduler assigns the highest weight to back ends
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with the most available capacity.</para>
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</listitem>
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</orderedlist>
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<para>The scheduler uses filters and weights to pick the best
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back end to handle the request. The scheduler uses volume
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types to explicitly create volumes on specific back
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ends.</para>
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<!-- TODO: when filter/weighing scheduler documentation will be up, a ref should be added here -->
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</simplesect>
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<simplesect>
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<title>Volume type</title>
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<para>Before using it, a volume type has to be declared to
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Block Storage. This can be done by the following
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command:</para>
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<screen><prompt>$</prompt> <userinput>cinder --os-username admin --os-tenant-name admin type-create lvm</userinput></screen>
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<para>Then, an extra-specification has to be created to link
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the volume type to a back end name. Run this
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command:</para>
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<screen><prompt>$</prompt> <userinput>cinder --os-username admin --os-tenant-name admin type-key lvm set volume_backend_name=LVM_iSCSI</userinput></screen>
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<para>This example creates a <literal>lvm</literal> volume
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type with <literal>volume_backend_name=LVM_iSCSI</literal>
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as extra-specifications.</para>
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<para>Create another volume type:</para>
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<screen><prompt>$</prompt> <userinput>cinder --os-username admin --os-tenant-name admin type-create lvm_gold</userinput></screen>
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<screen><prompt>$</prompt> <userinput>cinder --os-username admin --os-tenant-name admin type-key lvm_gold set volume_backend_name=LVM_iSCSI_b</userinput></screen>
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<para>This second volume type is named
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<literal>lvm_gold</literal> and has
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<literal>LVM_iSCSI_b</literal> as back end
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name.</para>
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<note>
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<para>To list the extra-specifications, use this
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command:</para>
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<screen><prompt>$</prompt> <userinput>cinder --os-username admin --os-tenant-name admin extra-specs-list</userinput></screen>
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</note>
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<note>
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<para>If a volume type points to a
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<literal>volume_backend_name</literal> that does
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not exist in the Block Storage configuration, the
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<literal>filter_scheduler</literal> returns an
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error that it cannot find a valid host with the
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suitable back end.</para>
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</note>
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</simplesect>
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<simplesect>
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<title>Usage</title>
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<para>When you create a volume, you must specify the volume
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type. The extra-specifications of the volume type are used
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to determine which back end has to be used.
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<screen><prompt>$</prompt> <userinput>cinder create --volume_type lvm --display_name test_multi_backend 1</userinput></screen>
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Considering the <literal>cinder.conf</literal> described
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previously, the scheduler creates this volume on
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<literal>lvmdriver-1</literal> or
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<literal>lvmdriver-2</literal>.</para>
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<screen><prompt>$</prompt> <userinput>cinder create --volume_type lvm_gold --display_name test_multi_backend 1</userinput></screen>
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<para>This second volume is created on
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<literal>lvmdriver-3</literal>.</para>
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</simplesect>
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</section>
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