mirror of
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2e14861224
Disk manufacturers are fond of quoting sizes in powers of 10,
rather than powers of 2 (after all, 2.1 GB sounds larger than
2.0 GiB, even though the exact opposite is true). So, we might
as well follow coreutils' lead in supporting three types of
suffix: single letter ${u} (which we already had) and ${u}iB
for the power of 2, and ${u}B for power of 10.
Additionally, it is impossible to create a file with more than
2**63 bytes, since off_t is signed (if you have enough storage
to even create one 8EiB file, I'm jealous). This now reports
failure up front rather than down the road when the kernel
finally refuses an impossible size.
* docs/schemas/basictypes.rng (unit): Add suffixes.
* src/conf/storage_conf.c (virStorageSize): Use new function.
* docs/formatstorage.html.in: Document it.
* tests/storagevolxml2xmlin/vol-file-backing.xml: Test it.
* tests/storagevolxml2xmlin/vol-file.xml: Likewise.
419 lines
19 KiB
HTML
419 lines
19 KiB
HTML
<html>
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<body>
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<h1>Storage pool and volume XML format</h1>
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<ul id="toc"></ul>
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<h2><a name="StoragePool">Storage pool XML</a></h2>
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<p>
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Although all storage pool backends share the same public APIs and
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XML format, they have varying levels of capabilities. Some may
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allow creation of volumes, others may only allow use of pre-existing
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volumes. Some may have constraints on volume size, or placement.
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</p>
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<p>
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The top level tag for a storage pool document is 'pool'. It has
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a single attribute <code>type</code>, which is one of <code>dir</code>,
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<code>fs</code>,<code>netfs</code>,<code>disk</code>,<code>iscsi</code>,
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<code>logical</code>. This corresponds to the storage backend drivers
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listed further along in this document.
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The storage pool XML format is available <span class="since">since 0.4.1</span>
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</p>
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<h3><a name="StoragePoolFirst">General metadata</a></h3>
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<pre>
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<pool type="iscsi">
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<name>virtimages</name>
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<uuid>3e3fce45-4f53-4fa7-bb32-11f34168b82b</uuid>
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<allocation>10000000</allocation>
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<capacity>50000000</capacity>
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<available>40000000</available>
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...</pre>
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<dl>
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<dt><code>name</code></dt>
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<dd>Providing a name for the pool which is unique to the host.
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This is mandatory when defining a pool. <span class="since">Since 0.4.1</span></dd>
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<dt><code>uuid</code></dt>
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<dd>Providing an identifier for the pool which is globally unique.
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This is optional when defining a pool, a UUID will be generated if
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omitted. <span class="since">Since 0.4.1</span></dd>
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<dt><code>allocation</code></dt>
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<dd>Providing the total storage allocation for the pool. This may
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be larger than the sum of the allocation of all volumes due to
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metadata overhead. This value is in bytes. This is not applicable
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when creating a pool. <span class="since">Since 0.4.1</span></dd>
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<dt><code>capacity</code></dt>
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<dd>Providing the total storage capacity for the pool. Due to
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underlying device constraints it may not be possible to use the
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full capacity for storage volumes. This value is in bytes. This
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is not applicable when creating a pool. <span class="since">Since 0.4.1</span></dd>
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<dt><code>available</code></dt>
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<dd>Providing the free space available for allocating new volumes
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in the pool. Due to underlying device constraints it may not be
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possible to allocate the entire free space to a single volume.
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This value is in bytes. This is not applicable when creating a
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pool. <span class="since">Since 0.4.1</span></dd>
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</dl>
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<h3><a name="StoragePoolSource">Source elements</a></h3>
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<p>
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A single <code>source</code> element is contained within the top level
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<code>pool</code> element. This tag is used to describe the source of
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the storage pool. It can contain the following child elements:
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</p>
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<pre>
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...
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<source>
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<host name="iscsi.example.com"/>
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<device path="demo-target"/>
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<vendor name="Acme"/>
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<product name="model"/>
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</source>
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...</pre>
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<dl>
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<dt><code>device</code></dt>
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<dd>Provides the source for pools backed by physical devices.
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May be repeated multiple times depending on backend driver. Contains
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a single attribute <code>path</code> which is the fully qualified
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path to the block device node. <span class="since">Since 0.4.1</span></dd>
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<dt><code>directory</code></dt>
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<dd>Provides the source for pools backed by directories. May
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only occur once. Contains a single attribute <code>path</code>
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which is the fully qualified path to the block device node.
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<span class="since">Since 0.4.1</span></dd>
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<dt><code>adapter</code></dt>
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<dd>Provides the source for pools backed by SCSI adapters. May
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only occur once. Contains a single attribute <code>name</code>
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which is the SCSI adapter name (ex. "host1").
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<span class="since">Since 0.6.2</span></dd>
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<dt><code>host</code></dt>
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<dd>Provides the source for pools backed by storage from a
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remote server. Will be used in combination with a <code>directory</code>
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or <code>device</code> element. Contains an attribute <code>name</code>
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which is the hostname or IP address of the server. May optionally
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contain a <code>port</code> attribute for the protocol specific
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port number. <span class="since">Since 0.4.1</span></dd>
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<dt><code>name</code></dt>
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<dd>Provides the source for pools backed by storage from a
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named element (e.g., a logical volume group name).
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remote server. Contains a string identifier.
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<span class="since">Since 0.4.5</span></dd>
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<dt><code>format</code></dt>
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<dd>Provides information about the format of the pool. This
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contains a single attribute <code>type</code> whose value is
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backend specific. This is typically used to indicate filesystem
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type, or network filesystem type, or partition table type, or
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LVM metadata type. All drivers are required to have a default
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value for this, so it is optional. <span class="since">Since 0.4.1</span></dd>
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<dt><code>vendor</code></dt>
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<dd>Provides optional information about the vendor of the
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storage device. This contains a single
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attribute <code>name</code> whose value is backend
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specific. <span class="since">Since 0.8.4</span></dd>
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<dt><code>product</code></dt>
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<dd>Provides an optional product name of the storage device.
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This contains a single attribute <code>name</code> whose value
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is backend specific. <span class="since">Since 0.8.4</span></dd>
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</dl>
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<h3><a name="StoragePoolTarget">Target elements</a></h3>
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<p>
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A single <code>target</code> element is contained within the top level
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<code>pool</code> element. This tag is used to describe the mapping of
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the storage pool into the host filesystem. It can contain the following
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child elements:
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</p>
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<pre>
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...
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<target>
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<path>/dev/disk/by-path</path>
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<permissions>
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<owner>107</owner>
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<group>107</group>
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<mode>0744</mode>
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<label>virt_image_t</label>
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</permissions>
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<encryption type='...'>
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...
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</encryption>
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</target>
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</pool></pre>
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<dl>
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<dt><code>path</code></dt>
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<dd>Provides the location at which the pool will be mapped into
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the local filesystem namespace. For a filesystem/directory based
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pool it will be the name of the directory in which volumes will
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be created. For device based pools it will be the name of the directory in which
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devices nodes exist. For the latter <code>/dev/</code> may seem
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like the logical choice, however, devices nodes there are not
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guaranteed stable across reboots, since they are allocated on
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demand. It is preferable to use a stable location such as one
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of the <code>/dev/disk/by-{path,id,uuid,label</code> locations.
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<span class="since">Since 0.4.1</span>
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</dd>
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<dt><code>permissions</code></dt>
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<dd>Provides information about the default permissions to use
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when creating volumes. This is currently only useful for directory
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or filesystem based pools, where the volumes allocated are simple
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files. For pools where the volumes are device nodes, the hotplug
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scripts determine permissions. It contains 4 child elements. The
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<code>mode</code> element contains the octal permission set. The
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<code>owner</code> element contains the numeric user ID. The <code>group</code>
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element contains the numeric group ID. The <code>label</code> element
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contains the MAC (eg SELinux) label string.
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<span class="since">Since 0.4.1</span>
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</dd>
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<dt><code>encryption</code></dt>
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<dd>If present, specifies how the volume is encrypted. See
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the <a href="formatstorageencryption.html">Storage Encryption</a> page
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for more information.
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</dd>
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</dl>
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<h3><a name="StoragePoolExtents">Device extents</a></h3>
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<p>
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If a storage pool exposes information about its underlying
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placement / allocation scheme, the <code>device</code> element
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within the <code>source</code> element may contain information
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about its available extents. Some pools have a constraint that
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a volume must be allocated entirely within a single constraint
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(eg disk partition pools). Thus the extent information allows an
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application to determine the maximum possible size for a new
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volume
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</p>
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<p>
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For storage pools supporting extent information, within each
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<code>device</code> element there will be zero or more <code>freeExtent</code>
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elements. Each of these elements contains two attributes, <code>start</code>
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and <code>end</code> which provide the boundaries of the extent on the
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device, measured in bytes. <span class="since">Since 0.4.1</span>
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</p>
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<h2><a name="StorageVol">Storage volume XML</a></h2>
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<p>
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A storage volume will be either a file or a device node.
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The storage volume XML format is available <span class="since">since 0.4.1</span>
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</p>
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<h3><a name="StorageVolFirst">General metadata</a></h3>
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<pre>
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<volume>
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<name>sparse.img</name>
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<key>/var/lib/xen/images/sparse.img</key>
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<allocation>0</allocation>
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<capacity unit="T">1</capacity>
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...</pre>
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<dl>
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<dt><code>name</code></dt>
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<dd>Providing a name for the volume which is unique to the pool.
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This is mandatory when defining a volume. <span class="since">Since 0.4.1</span></dd>
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<dt><code>key</code></dt>
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<dd>Providing an identifier for the volume which is globally unique.
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This cannot be set when creating a volume: it is always generated.
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<span class="since">Since 0.4.1</span></dd>
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<dt><code>allocation</code></dt>
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<dd>Providing the total storage allocation for the volume. This
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may be smaller than the logical capacity if the volume is sparsely
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allocated. It may also be larger than the logical capacity if the
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volume has substantial metadata overhead. This value is in bytes.
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If omitted when creating a volume, the volume will be fully
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allocated at time of creation. If set to a value smaller than the
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capacity, the pool has the <strong>option</strong> of deciding
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to sparsely allocate a volume. It does not have to honour requests
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for sparse allocation though.<br/>
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<br/>
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By default this is specified in bytes, but an optional attribute
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<code>unit</code> can be specified to adjust the passed value.
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Values can be: 'B' or 'bytes' for bytes, 'KB' (kilobytes,
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10<sup>3</sup> or 1000 bytes), 'K' or 'KiB' (kibibytes,
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2<sup>10</sup> or 1024 bytes), 'MB' (megabytes, 10<sup>6</sup>
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or 1,000,000 bytes), 'M' or 'MiB' (mebibytes, 2<sup>20</sup>
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or 1,048,576 bytes), 'GB' (gigabytes, 10<sup>9</sup> or
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1,000,000,000 bytes), 'G' or 'GiB' (gibibytes, 2<sup>30</sup>
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or 1,073,741,824 bytes), 'TB' (terabytes, 10<sup>12</sup> or
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1,000,000,000,000 bytes), 'T' or 'TiB' (tebibytes,
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2<sup>40</sup> or 1,099,511,627,776 bytes), 'PB' (petabytes,
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10<sup>15</sup> or 1,000,000,000,000,000 bytes), 'P' or 'PiB'
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(pebibytes, 2<sup>50</sup> or 1,125,899,906,842,624 bytes),
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'EB' (exabytes, 10<sup>18</sup> or 1,000,000,000,000,000,000
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bytes), or 'E' or 'EiB' (exbibytes, 2<sup>60</sup> or
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1,152,921,504,606,846,976 bytes). <span class="since">Since
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0.4.1, multi-character <code>unit</code> since
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0.9.11</span></dd>
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<dt><code>capacity</code></dt>
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<dd>Providing the logical capacity for the volume. This value is
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in bytes by default, but a <code>unit</code> attribute can be
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specified with the same semantics as for <code>allocation</code>
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This is compulsory when creating a volume.
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<span class="since">Since 0.4.1</span></dd>
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<dt><code>source</code></dt>
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<dd>Provides information about the underlying storage allocation
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of the volume. This may not be available for some pool types.
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<span class="since">Since 0.4.1</span></dd>
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<dt><code>target</code></dt>
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<dd>Provides information about the representation of the volume
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on the local host. <span class="since">Since 0.4.1</span></dd>
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</dl>
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<h3><a name="StorageVolTarget">Target elements</a></h3>
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<p>
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A single <code>target</code> element is contained within the top level
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<code>volume</code> element. This tag is used to describe the mapping of
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the storage volume into the host filesystem. It can contain the following
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child elements:
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</p>
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<pre>
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...
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<target>
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<path>/var/lib/virt/images/sparse.img</path>
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<format type='qcow2'/>
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<permissions>
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<owner>107</owner>
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<group>107</group>
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<mode>0744</mode>
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<label>virt_image_t</label>
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</permissions>
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</target></pre>
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<dl>
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<dt><code>path</code></dt>
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<dd>Provides the location at which the volume can be accessed on
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the local filesystem, as an absolute path. This is a readonly
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attribute, so shouldn't be specified when creating a volume.
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<span class="since">Since 0.4.1</span></dd>
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<dt><code>format</code></dt>
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<dd>Provides information about the pool specific volume format.
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For disk pools it will provide the partition type. For filesystem
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or directory pools it will provide the file format type, eg cow,
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qcow, vmdk, raw. If omitted when creating a volume, the pool's
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default format will be used. The actual format is specified via
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the <code>type</code> attribute. Consult the pool-specific docs for
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the list of valid values. <span class="since">Since 0.4.1</span></dd>
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<dt><code>permissions</code></dt>
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<dd>Provides information about the default permissions to use
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when creating volumes. This is currently only useful for directory
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or filesystem based pools, where the volumes allocated are simple
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files. For pools where the volumes are device nodes, the hotplug
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scripts determine permissions. It contains 4 child elements. The
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<code>mode</code> element contains the octal permission set. The
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<code>owner</code> element contains the numeric user ID. The <code>group</code>
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element contains the numeric group ID. The <code>label</code> element
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contains the MAC (eg SELinux) label string.
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<span class="since">Since 0.4.1</span>
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</dd>
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</dl>
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<h3><a name="StorageVolBacking">Backing store elements</a></h3>
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<p>
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A single <code>backingStore</code> element is contained within the top level
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<code>volume</code> element. This tag is used to describe the optional copy
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on write, backing store for the storage volume. It can contain the following
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child elements:
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</p>
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<pre>
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...
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<backingStore>
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<path>/var/lib/virt/images/master.img</path>
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<format type='raw'/>
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<permissions>
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<owner>107</owner>
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<group>107</group>
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<mode>0744</mode>
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<label>virt_image_t</label>
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</permissions>
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</backingStore>
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</volume></pre>
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<dl>
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<dt><code>path</code></dt>
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<dd>Provides the location at which the backing store can be accessed on
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the local filesystem, as an absolute path. If omitted, there is no
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backing store for this volume.
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<span class="since">Since 0.6.0</span></dd>
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<dt><code>format</code></dt>
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<dd>Provides information about the pool specific backing store format.
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For disk pools it will provide the partition type. For filesystem
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or directory pools it will provide the file format type, eg cow,
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qcow, vmdk, raw. The actual format is specified via the type attribute.
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Consult the pool-specific docs for the list of valid
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values. Most file formats require a backing store of the same format,
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however, the qcow2 format allows a different backing store format.
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<span class="since">Since 0.6.0</span></dd>
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<dt><code>permissions</code></dt>
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<dd>Provides information about the permissions of the backing file.
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It contains 4 child elements. The
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<code>mode</code> element contains the octal permission set. The
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<code>owner</code> element contains the numeric user ID. The <code>group</code>
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element contains the numeric group ID. The <code>label</code> element
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contains the MAC (eg SELinux) label string.
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<span class="since">Since 0.6.0</span>
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</dd>
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</dl>
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<h2><a name="examples">Example configuration</a></h2>
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<p>
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Here are a couple of examples, for a more complete set demonstrating
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every type of storage pool, consult the <a href="storage.html">storage driver page</a>
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</p>
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<h3><a name="exampleFile">File based storage pool</a></h3>
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<pre>
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<pool type="dir">
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<name>virtimages</name>
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<target>
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<path>/var/lib/virt/images</path>
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</target>
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</pool></pre>
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<h3><a name="exampleISCSI">iSCSI based storage pool</a></h3>
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<pre>
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<pool type="iscsi">
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<name>virtimages</name>
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<source>
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<host name="iscsi.example.com"/>
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<device path="demo-target"/>
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</source>
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<target>
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<path>/dev/disk/by-path</path>
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</target>
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</pool></pre>
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<h3><a name="exampleVol">Storage volume</a></h3>
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<pre>
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<volume>
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<name>sparse.img</name>
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<allocation>0</allocation>
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<capacity unit="T">1</capacity>
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<target>
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<path>/var/lib/virt/images/sparse.img</path>
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<permissions>
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<owner>107</owner>
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<group>107</group>
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<mode>0744</mode>
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<label>virt_image_t</label>
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</permissions>
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</target>
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</volume></pre>
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</body>
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</html>
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