260 lines
15 KiB
XML
260 lines
15 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE section [
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<!ENTITY % openstack SYSTEM "entities/openstack.ent">
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%openstack;
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]>
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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="host-aggregates">
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<title>Host aggregates</title>
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<para>Host aggregates are a mechanism to further partition an
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availability zone; while availability zones are visible to
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users, host aggregates are only visible to administrators.
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Host Aggregates provide a mechanism to allow administrators to
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assign key-value pairs to groups of machines. Each node can
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have multiple aggregates, each aggregate can have multiple
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key-value pairs, and the same key-value pair can be assigned
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to multiple aggregates. This information can be used in the
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scheduler to enable advanced scheduling, to set up hypervisor
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resource pools or to define logical groups for
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migration.</para>
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<simplesect>
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<title>Command-line interface</title>
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<para>The <command>nova</command> command-line tool supports
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the following aggregate-related commands. <variablelist>
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<varlistentry>
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<term><command>nova
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aggregate-list</command></term>
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<listitem>
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<para>Print a list of all aggregates.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>nova aggregate-create
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<replaceable><name></replaceable>
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<replaceable><availability-zone></replaceable></command></term>
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<listitem>
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<para>Create a new aggregate named
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<replaceable><name></replaceable>
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in availability zone
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<replaceable><availability-zone></replaceable>.
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Returns the ID of the newly created
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aggregate. Hosts can be made available to
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multiple availability zones, but
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administrators should be careful when
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adding the host to a different host
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aggregate within the same availability
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zone and pay attention when using the
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<command>aggregate-set-metadata</command>
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and <command>aggregate-update</command>
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commands to avoid user confusion when they
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boot instances in different availability
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zones. An error occurs if you cannot add a
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particular host to an aggregate zone for
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which it is not intended.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>nova aggregate-delete
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<replaceable><id></replaceable></command></term>
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<listitem>
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<para>Delete an aggregate with id
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<replaceable><id></replaceable>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>nova aggregate-details
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<replaceable><id></replaceable></command></term>
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<listitem>
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<para>Show details of the aggregate with id
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<replaceable><id></replaceable>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>nova aggregate-add-host
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<replaceable><id></replaceable>
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<replaceable><host></replaceable></command></term>
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<listitem>
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<para>Add host with name
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<replaceable><host></replaceable>
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to aggregate with id
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<replaceable><id></replaceable>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>nova aggregate-remove-host
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<replaceable><id></replaceable>
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<replaceable><host></replaceable></command></term>
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<listitem>
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<para>Remove the host with name
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<replaceable><host></replaceable>
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from the aggregate with id
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<replaceable><id></replaceable>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>nova aggregate-set-metadata
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<replaceable><id></replaceable>
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<replaceable><key=value></replaceable>
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[<replaceable><key=value></replaceable>
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...]</command></term>
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<listitem>
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<para>Add or update metadata (key-value pairs)
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associated with the aggregate with id
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<replaceable><id></replaceable>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>nova aggregate-update
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<replaceable><id></replaceable>
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<replaceable><name></replaceable>
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[<replaceable><availability_zone></replaceable>]</command></term>
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<listitem>
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<para>Update the name and availability zone
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(optional) for the aggregate.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>nova host-list</command></term>
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<listitem>
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<para>List all hosts by service.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>nova host-update --maintenance
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[enable | disable]</command></term>
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<listitem>
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<para>Put/resume host into/from
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maintenance.</para>
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</listitem>
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</varlistentry>
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</variablelist></para>
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<note>
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<para>Only administrators can access these commands. If
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you try to use these commands and the user name and
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tenant that you use to access the Compute service do
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not have the <literal>admin</literal> role or the
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appropriate privileges, these errors occur:</para>
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<screen><computeroutput>ERROR: Policy doesn't allow compute_extension:aggregates to be performed. (HTTP 403) (Request-ID: req-299fbff6-6729-4cef-93b2-e7e1f96b4864)
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</computeroutput></screen>
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<screen><computeroutput>ERROR: Policy doesn't allow compute_extension:hosts to be performed. (HTTP 403) (Request-ID: req-ef2400f6-6776-4ea3-b6f1-7704085c27d1)
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</computeroutput></screen>
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</note>
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</simplesect>
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<simplesect>
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<title>Configure scheduler to support host aggregates</title>
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<para>One common use case for host aggregates is when you want
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to support scheduling instances to a subset of compute
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hosts because they have a specific capability. For
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example, you may want to allow users to request compute
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hosts that have SSD drives if they need access to faster
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disk I/O, or access to compute hosts that have GPU cards
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to take advantage of GPU-accelerated code.</para>
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<para>To configure the scheduler to support host aggregates,
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the <literal>scheduler_default_filters</literal>
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configuration option must contain the
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<literal>AggregateInstanceExtraSpecsFilter</literal>
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in addition to the other filters used by the scheduler.
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Add the following line to
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<filename>/etc/nova/nova.conf</filename> on the host
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that runs the <systemitem class="service"
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>nova-scheduler</systemitem> service to enable host
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aggregates filtering, as well as the other filters that
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are typically
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enabled:<programlisting language="ini">scheduler_default_filters=AggregateInstanceExtraSpecsFilter,AvailabilityZoneFilter,RamFilter,ComputeFilter</programlisting></para>
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</simplesect>
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<simplesect>
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<title>Example: Specify compute hosts with SSDs</title>
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<para>This example configures the Compute service to enable
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users to request nodes that have solid-state drives
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(SSDs). You create a <literal>fast-io</literal> host
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aggregate in the <literal>nova</literal> availability zone
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and you add the <literal>ssd=true</literal> key-value pair
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to the aggregate. Then, you add the
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<literal>node1</literal>, and <literal>node2</literal>
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compute nodes to it.</para>
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<screen><prompt>$</prompt> <userinput>nova aggregate-create fast-io nova</userinput>
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<computeroutput>+----+---------+-------------------+-------+----------+
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| Id | Name | Availability Zone | Hosts | Metadata |
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+----+---------+-------------------+-------+----------+
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| 1 | fast-io | nova | | |
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+----+---------+-------------------+-------+----------+</computeroutput>
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<prompt>$</prompt> <userinput>nova aggregate-set-metadata 1 ssd=true</userinput>
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<computeroutput>+----+---------+-------------------+-------+-------------------+
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| Id | Name | Availability Zone | Hosts | Metadata |
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+----+---------+-------------------+-------+-------------------+
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| 1 | fast-io | nova | [] | {u'ssd': u'true'} |
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+----+---------+-------------------+-------+-------------------+</computeroutput>
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<prompt>$</prompt> <userinput>nova aggregate-add-host 1 node1</userinput>
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<computeroutput>+----+---------+-------------------+-----------+-------------------+
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| Id | Name | Availability Zone | Hosts | Metadata |
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+----+---------+-------------------+------------+-------------------+
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| 1 | fast-io | nova | [u'node1'] | {u'ssd': u'true'} |
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+----+---------+-------------------+------------+-------------------+</computeroutput>
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<prompt>$</prompt> <userinput>nova aggregate-add-host 1 node2</userinput>
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<computeroutput>+----+---------+-------------------+---------------------+-------------------+
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| Id | Name | Availability Zone | Hosts | Metadata |
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+----+---------+-------------------+----------------------+-------------------+
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| 1 | fast-io | nova | [u'node1', u'node2'] | {u'ssd': u'true'} |
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+----+---------+-------------------+----------------------+-------------------+</computeroutput></screen>
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<para>Use the <command>nova flavor-create</command> command to create
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the <replaceable>ssd.large</replaceable> flavor called with an ID of
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6, 8 GB of RAM, 80 GB root disk, and four vCPUs.</para>
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<screen><prompt>$</prompt> <userinput>nova flavor-create <replaceable>ssd.large</replaceable> <replaceable>6</replaceable> <replaceable>8192</replaceable> <replaceable>80</replaceable> <replaceable>4</replaceable></userinput>
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<computeroutput>+----+-----------+-----------+------+-----------+------+-------+-------------+-----------+-------------+
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| ID | Name | Memory_MB | Disk | Ephemeral | Swap | VCPUs | RXTX_Factor | Is_Public | extra_specs |
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+----+-----------+-----------+------+-----------+------+-------+-------------+-----------+-------------+
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| 6 | ssd.large | 8192 | 80 | 0 | | 4 | 1 | True | {} |
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+----+-----------+-----------+------+-----------+------+-------+-------------+-----------+-------------+</computeroutput></screen>
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<para>Once the flavor is created, specify one or more
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key-value pairs that match the key-value pairs on the host
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aggregates. In this case, that is the
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<replaceable>ssd=true</replaceable> key-value pair. Setting a
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key-value pair on a flavor is done using the <command>nova
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flavor-key</command> command.</para>
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<screen><prompt>$</prompt> <userinput>nova flavor-key <replaceable>ssd.large</replaceable> set <replaceable>ssd=true</replaceable></userinput></screen>
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<para>Once it is set, you should see the
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<literal>extra_specs</literal> property of the
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<literal>ssd.large</literal> flavor populated with a
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key of <literal>ssd</literal> and a corresponding value of
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<literal>true</literal>.</para>
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<screen><prompt>$</prompt> <userinput>nova flavor-show ssd.large</userinput>
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<computeroutput>+----------------------------+-------------------+
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| Property | Value |
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+----------------------------+-------------------+
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| OS-FLV-DISABLED:disabled | False |
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| OS-FLV-EXT-DATA:ephemeral | 0 |
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| disk | 80 |
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| extra_specs | {u'ssd': u'true'} |
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| id | 6 |
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| name | ssd.large |
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| os-flavor-access:is_public | True |
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| ram | 8192 |
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| rxtx_factor | 1.0 |
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| swap | |
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| vcpus | 4 |
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+----------------------------+-------------------+</computeroutput></screen>
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<para>Now, when a user requests an instance with the
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<literal>ssd.large</literal> flavor, the scheduler
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only considers hosts with the <literal>ssd=true</literal>
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key-value pair. In this example, these are
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<literal>node1</literal> and
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<literal>node2</literal>.</para>
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</simplesect>
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<simplesect>
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<title>XenServer hypervisor pools to support live
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migration</title>
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<para>When using the XenAPI-based hypervisor, the Compute
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service uses host aggregates to manage XenServer Resource
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pools, which are used in supporting live migration.
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<!--See <link
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linkend="configuring-migrations-xenserver-shared-storage">Configuring Migrations</link> for details on how to
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create these kinds of host aggregates to support live migration. --></para>
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</simplesect>
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</section>
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