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238 lines
10 KiB
HTML
238 lines
10 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>
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<li>
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<a href="#StoragePool">Storage pool XML</a>
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<ul>
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<li>
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<a href="#StoragePoolFirst">First level elements</a>
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</li>
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<li>
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<a href="#StoragePoolSource">Source elements</a>
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</li>
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<li>
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<a href="#StoragePoolTarget">Target elements</a>
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</li>
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<li>
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<a href="#StoragePoolExtents">Device extents</a>
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</li>
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</ul>
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</li>
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<li>
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<a href="#StorageVol">Storage volume XML</a>
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<ul>
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<li>
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<a href="#StorageVolFirst">First level elements</a>
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</li>
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<li>
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<a href="#StorageVolSource">Source elements</a>
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</li>
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<li>
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<a href="#StorageVolTarget">Target elements</a>
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</li>
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</ul>
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</li>
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</ul>
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<h3>
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<a name="StoragePool" id="StoragePool">Storage pool XML</a>
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</h3>
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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>The is 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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</p>
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<h4>
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<a name="StoragePoolFirst" id="StoragePoolFirst">First level elements</a>
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</h4>
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<dl>
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<dt>name</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</dd>
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<dt>uuid</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</dd>
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<dt>allocation</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.</dd>
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<dt>capacity</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.</dd>
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<dt>available</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.</dd>
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<dt>source</dt>
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<dd>Provides information about the source of the pool, such as
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the underlying host devices, or remote server</dd>
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<dt>target</dt>
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<dd>Provides information about the representation of the pool
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on the local host.</dd>
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</dl>
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<h4>
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<a name="StoragePoolSource" id="StoragePoolSource">Source elements</a>
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</h4>
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<dl>
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<dt>device</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.</dd>
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<dt>directory</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.</dd>
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<dt>host</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.</code></code></dd>
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<dt>format</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.</dd>
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</dl>
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<h4>
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<a name="StoragePoolTarget" id="StoragePoolTarget">Target elements</a>
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</h4>
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<dl>
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<dt>path</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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</dd>
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<dt>permissions</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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</dd>
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</dl>
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<h4>
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<a name="StoragePoolExtents" id="StoragePoolExtents">Device extents</a>
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</h4>
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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.
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</p>
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<h3>
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<a name="StorageVol" id="StorageVol">Storage volume XML</a>
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</h3>
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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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</p>
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<h4>
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<a name="StorageVolFirst" id="StorageVolFirst">First level elements</a>
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</h4>
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<dl>
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<dt>name</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</dd>
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<dt>uuid</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</dd>
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<dt>allocation</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.</dd>
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<dt>capacity</dt>
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<dd>Providing the logical capacity for the volume. This value is
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in bytes. This is compulsory when creating a volume</dd>
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<dt>source</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.</dd>
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<dt>target</dt>
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<dd>Provides information about the representation of the volume
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on the local host.</dd>
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</dl>
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<h4>
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<a name="StorageVolTarget" id="StorageVolTarget">Target elements</a>
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</h4>
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<dl>
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<dt>path</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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</dd>
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<dt>format</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>. Consult the pool-specific docs for the
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list of valid values.</dd>
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<dt>permissions</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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</dd>
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</dl>
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</body>
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</html>
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