165 lines
8.4 KiB
XML
165 lines
8.4 KiB
XML
<section xml:id="NFS-driver" 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" version="5.0">
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<title>NFS driver</title>
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<para>The Network File System (NFS) is a distributed file system
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protocol originally developed by Sun Microsystems in 1984. An
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NFS server <emphasis>exports</emphasis> one or more of its
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file systems, known as <emphasis>shares</emphasis>. An NFS
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client can mount these exported shares on its own file system.
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You can perform file actions on this mounted remote file
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system as if the file system were local.</para>
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<section xml:id="nfs-driver-background">
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<title>How the NFS driver works</title>
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<para>The NFS driver, and other drivers based on it, work
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quite differently than a traditional block storage
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driver.</para>
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<para>The NFS driver does not actually allow an instance to
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access a storage device at the block level. Instead, files
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are created on an NFS share and mapped to instances, which
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emulates a block device. This works in a similar way to
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QEMU, which stores instances in the
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<filename>/var/lib/nova/instances</filename>
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directory.</para>
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</section>
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<section xml:id="nfs-driver-options">
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<title>Enable the NFS driver and related options</title>
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<para>To use Cinder with the NFS driver, first set the
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<literal>volume_driver</literal> in
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<filename>cinder.conf</filename>:</para>
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<programlisting>volume_driver=cinder.volume.drivers.nfs.NfsDriver</programlisting>
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<para>The following table contains the options supported by
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the NFS driver.</para>
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<xi:include
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href="../../../common/tables/cinder-storage_nfs.xml"/>
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<note>
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<para>As of the Icehouse release, the NFS driver (and other
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drivers based off it) will attempt to mount shares
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using version 4.1 of the NFS protocol (including pNFS). If the
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mount attempt is unsuccessful due to a lack of client or
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server support, a subsequent mount attempt that requests the
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default behavior of the <command>mount.nfs</command> command
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will be performed. On most distributions, the default behavior
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is to attempt mounting first with NFS v4.0, then silently fall
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back to NFS v3.0 if necessary. If the
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<option>nfs_mount_options</option> configuration option
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contains a request for a specific version of NFS to be used,
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or if specific options are specified in the shares
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configuration file specified by the
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<option>nfs_shares_config</option> configuration option, the
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mount will be attempted as requested with no subsequent
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attempts.</para>
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</note>
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</section>
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<section xml:id="nfs-driver-howto">
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<title>How to use the NFS driver</title>
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<procedure>
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<step>
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<para>Access to one or more NFS servers. Creating an
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NFS server is outside the scope of this document.
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This example assumes access to the following NFS
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servers and mount points:</para>
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<itemizedlist>
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<listitem>
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<para><literal>192.168.1.200:/storage</literal></para>
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</listitem>
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<listitem>
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<para><literal>192.168.1.201:/storage</literal></para>
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</listitem>
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<listitem>
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<para><literal>192.168.1.202:/storage</literal></para>
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</listitem>
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</itemizedlist>
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<para>This example demonstrates the use of with this
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driver with multiple NFS servers. Multiple servers
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are not required. One is usually enough.</para>
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</step>
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<step>
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<para>Add your list of NFS servers to the file you
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specified with the
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<literal>nfs_shares_config</literal> option.
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For example, if the value of this option was set
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to <literal>/etc/cinder/shares.txt</literal>,
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then:</para>
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<screen><prompt>#</prompt> <userinput>cat /etc/cinder/shares.txt</userinput>
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<computeroutput>192.168.1.200:/storage
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192.168.1.201:/storage
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192.168.1.202:/storage</computeroutput></screen>
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<para>Comments are allowed in this file. They begin
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with a <literal>#</literal>.</para>
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</step>
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<step>
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<para>Configure the
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<literal>nfs_mount_point_base</literal>
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option. This is a directory where <systemitem
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class="service">cinder-volume</systemitem>
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mounts all NFS shares stored in
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<literal>shares.txt</literal>. For this
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example, <literal>/var/lib/cinder/nfs</literal> is
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used. You can, of course, use the default value of
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<literal>$state_path/mnt</literal>.</para>
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</step>
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<step>
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<para>Start the <systemitem class="service"
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>cinder-volume</systemitem> service.
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<literal>/var/lib/cinder/nfs</literal> should
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now contain a directory for each NFS share
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specified in <literal>shares.txt</literal>. The
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name of each directory is a hashed name:</para>
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<screen><prompt>#</prompt> <userinput>ls /var/lib/cinder/nfs/</userinput>
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<computeroutput>...
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46c5db75dc3a3a50a10bfd1a456a9f3f
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...</computeroutput></screen>
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</step>
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<step>
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<para>You can now create volumes as you normally
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would:</para>
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<screen><prompt>$</prompt> <userinput>nova volume-create --display-name=myvol 5</userinput>
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<prompt>#</prompt> <userinput>ls /var/lib/cinder/nfs/46c5db75dc3a3a50a10bfd1a456a9f3f</userinput>
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<computeroutput>volume-a8862558-e6d6-4648-b5df-bb84f31c8935</computeroutput></screen>
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<para>This volume can also be attached and deleted
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just like other volumes. However, snapshotting is
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<emphasis>not</emphasis> supported.</para>
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</step>
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</procedure>
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</section>
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<simplesect xml:id="nfs-driver-notes">
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<title>NFS driver notes</title>
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<itemizedlist>
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<listitem>
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<para><systemitem class="service"
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>cinder-volume</systemitem> manages the
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mounting of the NFS shares as well as volume
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creation on the shares. Keep this in mind when
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planning your OpenStack architecture. If you have
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one master NFS server, it might make sense to only
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have one <systemitem class="service"
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>cinder-volume</systemitem> service to handle
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all requests to that NFS server. However, if that
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single server is unable to handle all requests,
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more than one <systemitem class="service"
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>cinder-volume</systemitem> service is needed
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as well as potentially more than one NFS
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server.</para>
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</listitem>
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<listitem>
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<para>Because data is stored in a file and not
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actually on a block storage device, you might not
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see the same IO performance as you would with a
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traditional block storage driver. Please test
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accordingly.</para>
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</listitem>
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<listitem>
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<para>Despite possible IO performance loss, having
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volume data stored in a file might be beneficial.
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For example, backing up volumes can be as easy as
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copying the volume files.</para>
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<note>
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<para>Regular IO flushing and syncing still
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stands.</para>
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</note>
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</listitem>
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</itemizedlist>
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</simplesect>
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</section>
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