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<h1>Storage pool and volume XML format</h1>
<ul><li>
<a href="#StoragePool">Storage pool XML</a>
<ul><li>
<a href="#StoragePoolFirst">General metadata</a>
</li><li>
<a href="#StoragePoolSource">Source elements</a>
</li><li>
<a href="#StoragePoolTarget">Target elements</a>
</li><li>
<a href="#StoragePoolExtents">Device extents</a>
</li></ul>
</li><li>
<a href="#StorageVol">Storage volume XML</a>
<ul><li>
<a href="#StorageVolFirst">General metadata</a>
</li><li>
<a href="#StorageVolTarget">Target elements</a>
</li><li>
<a href="#StorageVolBacking">Backing store elements</a>
</li></ul>
</li><li>
<a href="#examples">Example configuration</a>
<ul><li>
<a href="#exampleFile">File based storage pool</a>
</li><li>
<a href="#exampleISCSI">iSCSI based storage pool</a>
</li><li>
<a href="#exampleVol">Storage volume</a>
</li></ul>
</li></ul>
<h2>
<a name="StoragePool" shape="rect" id="StoragePool">Storage pool XML</a>
</h2>
<p>
Although all storage pool backends share the same public APIs and
XML format, they have varying levels of capabilities. Some may
allow creation of volumes, others may only allow use of pre-existing
volumes. Some may have constraints on volume size, or placement.
</p>
<p>
The top level tag for a storage pool document is 'pool'. It has
a single attribute <code>type</code>, which is one of <code>dir</code>,
<code>fs</code>, <code>netfs</code>, <code>disk</code>,
<code>iscsi</code>, <code>logical</code>, <code>scsi</code>
(all <span class="since">since 0.4.1</span>), <code>mpath</code>
(<span class="since">since 0.7.1</span>), <code>rbd</code>
(<span class="since">since 0.9.13</span>), <code>sheepdog</code>
(<span class="since">since 0.10.0</span>),
or <code>gluster</code> (<span class="since">since
1.2.0</span>). This corresponds to the
storage backend drivers listed further along in this document.
</p>
<h3>
<a name="StoragePoolFirst" shape="rect" id="StoragePoolFirst">General metadata</a>
</h3>
<pre xml:space="preserve">
<pool type="iscsi">
<name>virtimages</name>
<uuid>3e3fce45-4f53-4fa7-bb32-11f34168b82b</uuid>
<allocation>10000000</allocation>
<capacity>50000000</capacity>
<available>40000000</available>
...</pre>
<dl><dt><code>name</code></dt><dd>Providing a name for the pool which is unique to the host.
This is mandatory when defining a pool. <span class="since">Since 0.4.1</span></dd><dt><code>uuid</code></dt><dd>Providing an identifier for the pool which is globally unique.
This is optional when defining a pool, a UUID will be generated if
omitted. <span class="since">Since 0.4.1</span></dd><dt><code>allocation</code></dt><dd>Providing the total storage allocation for the pool. This may
be larger than the sum of the allocation of all volumes due to
metadata overhead. This value is in bytes. This is not applicable
when creating a pool. <span class="since">Since 0.4.1</span></dd><dt><code>capacity</code></dt><dd>Providing the total storage capacity for the pool. Due to
underlying device constraints it may not be possible to use the
full capacity for storage volumes. This value is in bytes. This
is not applicable when creating a pool. <span class="since">Since 0.4.1</span></dd><dt><code>available</code></dt><dd>Providing the free space available for allocating new volumes
in the pool. Due to underlying device constraints it may not be
possible to allocate the entire free space to a single volume.
This value is in bytes. This is not applicable when creating a
pool. <span class="since">Since 0.4.1</span></dd></dl>
<h3>
<a name="StoragePoolSource" shape="rect" id="StoragePoolSource">Source elements</a>
</h3>
<p>
A single <code>source</code> element is contained within the top level
<code>pool</code> element. This tag is used to describe the source of
the storage pool. The set of child elements that it will contain
depend on the pool type, but come from the following child elements:
</p>
<pre xml:space="preserve">
...
<source>
<host name="iscsi.example.com"/>
<device path="demo-target"/>
<auth type='chap' username='myname'>
<secret type='iscsi' usage='mycluster_myname'/>
</auth>
<vendor name="Acme"/>
<product name="model"/>
</source>
...</pre>
<pre xml:space="preserve">
...
<source>
<adapter type='fc_host' parent='scsi_host5' wwnn='20000000c9831b4b' wwpn='10000000c9831b4b'/>
</source>
...</pre>
<dl><dt><code>device</code></dt><dd>Provides the source for pools backed by physical devices
(pool types <code>fs</code>, <code>logical</code>, <code>disk</code>,
<code>iscsi</code>).
May be repeated multiple times depending on backend driver. Contains
a single attribute <code>path</code> which is the fully qualified
path to the block device node. <span class="since">Since 0.4.1</span></dd><dt><code>dir</code></dt><dd>Provides the source for pools backed by directories (pool
type <code>dir</code>), or optionally to select a subdirectory
within a pool that resembles a filesystem (pool
type <code>gluster</code>). May
only occur once. Contains a single attribute <code>path</code>
which is the fully qualified path to the backing directory.
<span class="since">Since 0.4.1</span></dd><dt><code>adapter</code></dt><dd>Provides the source for pools backed by SCSI adapters (pool
type <code>scsi</code>). May
only occur once. Attribute <code>name</code> is the SCSI adapter
name (ex. "scsi_host1". NB, although a name such as "host1" is
still supported for backwards compatibility, it is not recommended).
Attribute <code>type</code> (<span class="since">1.0.5</span>)
specifies the adapter type. Valid values are "fc_host" and "scsi_host".
If omitted and the <code>name</code> attribute is specified, then it
defaults to "scsi_host". To keep backwards compatibility, the attribute
<code>type</code> is optional for the "scsi_host" adapter, but
mandatory for the "fc_host" adapter. Attributes <code>wwnn</code>
(Word Wide Node Name) and <code>wwpn</code> (Word Wide Port Name)
(<span class="since">1.0.4</span>) are used by the "fc_host" adapter
to uniquely identify the device in the Fibre Channel storage fabric
(the device can be either a HBA or vHBA). Both wwnn and wwpn should
be specified (See command 'virsh nodedev-dumpxml' to known how to get
wwnn/wwpn of a (v)HBA). The optional attribute <code>parent</code>
(<span class="since">1.0.4</span>) specifies the parent device for
the "fc_host" adapter.
<span class="since">Since 0.6.2</span></dd><dt><code>host</code></dt><dd>Provides the source for pools backed by storage from a
remote server (pool types <code>netfs</code>, <code>iscsi</code>,
<code>rbd</code>, <code>sheepdog</code>, <code>gluster</code>). Will be
used in combination with a <code>directory</code>
or <code>device</code> element. Contains an attribute <code>name</code>
which is the hostname or IP address of the server. May optionally
contain a <code>port</code> attribute for the protocol specific
port number. <span class="since">Since 0.4.1</span></dd><dt><code>auth</code></dt><dd>If present, the <code>auth</code> element provides the
authentication credentials needed to access the source by the
setting of the <code>type</code> attribute (pool
types <code>iscsi</code>, <code>rbd</code>). The <code>type</code>
must be either "chap" or "ceph". Use "ceph" for
Ceph RBD (Rados Block Device) network sources and use "iscsi" for CHAP
(Challenge-Handshake Authentication Protocol) iSCSI
targets. Additionally a mandatory attribute
<code>username</code> identifies the username to use during
authentication as well as a sub-element <code>secret</code> with
a mandatory attribute <code>type</code>, to tie back to a
<a href="formatsecret.html" shape="rect">libvirt secret object</a> that
holds the actual password or other credentials. The domain XML
intentionally does not expose the password, only the reference
to the object that manages the password.
The <code>secret</code> element requires either a <code>uuid</code>
attribute with the UUID of the secret object or a <code>usage</code>
attribute matching the key that was specified in the
secret object. <span class="since">Since 0.9.7 for "ceph" and
1.1.1 for "chap"</span>
</dd><dt><code>name</code></dt><dd>Provides the source for pools backed by storage from a
named element (pool types <code>logical</code>, <code>rbd</code>,
<code>sheepdog</code>, <code>gluster</code>). Contains a
string identifier.
<span class="since">Since 0.4.5</span></dd><dt><code>format</code></dt><dd>Provides information about the format of the pool (pool
types <code>fs</code>, <code>netfs</code>, <code>disk</code>,
<code>logical</code>). This
contains a single attribute <code>type</code> whose value is
backend specific. This is typically used to indicate filesystem
type, or network filesystem type, or partition table type, or
LVM metadata type. All drivers are required to have a default
value for this, so it is optional. <span class="since">Since 0.4.1</span></dd><dt><code>vendor</code></dt><dd>Provides optional information about the vendor of the
storage device. This contains a single
attribute <code>name</code> whose value is backend
specific. <span class="since">Since 0.8.4</span></dd><dt><code>product</code></dt><dd>Provides an optional product name of the storage device.
This contains a single attribute <code>name</code> whose value
is backend specific. <span class="since">Since 0.8.4</span></dd></dl>
<h3>
<a name="StoragePoolTarget" shape="rect" id="StoragePoolTarget">Target elements</a>
</h3>
<p>
A single <code>target</code> element is contained within the top level
<code>pool</code> element for some types of pools (pool
types <code>dir</code>, <code>fs</code>, <code>netfs</code>,
<code>logical</code>, <code>disk</code>, <code>iscsi</code>,
<code>scsi</code>, <code>mpath</code>). This tag is used to
describe the mapping of
the storage pool into the host filesystem. It can contain the following
child elements:
</p>
<pre xml:space="preserve">
...
<target>
<path>/dev/disk/by-path</path>
<permissions>
<owner>107</owner>
<group>107</group>
<mode>0744</mode>
<label>virt_image_t</label>
</permissions>
<timestamps>
<atime>1341933637.273190990</atime>
<mtime>1341930622.047245868</mtime>
<ctime>1341930622.047245868</ctime>
</timestamps>
<encryption type='...'>
...
</encryption>
</target>
</pool></pre>
<dl><dt><code>path</code></dt><dd>Provides the location at which the pool will be mapped into
the local filesystem namespace. For a filesystem/directory based
pool it will be the name of the directory in which volumes will
be created. For device based pools it will be the name of the directory in which
devices nodes exist. For the latter <code>/dev/</code> may seem
like the logical choice, however, devices nodes there are not
guaranteed stable across reboots, since they are allocated on
demand. It is preferable to use a stable location such as one
of the <code>/dev/disk/by-{path,id,uuid,label</code> locations.
<span class="since">Since 0.4.1</span>
</dd><dt><code>permissions</code></dt><dd>This is currently only useful for directory or filesystem based
pools, which are mapped as a directory into the local filesystem
namespace. It provides information about the permissions to use for the
final directory when the pool is built. The
<code>mode</code> element contains the octal permission set. The
<code>owner</code> element contains the numeric user ID. The <code>group</code>
element contains the numeric group ID. The <code>label</code> element
contains the MAC (eg SELinux) label string.
<span class="since">Since 0.4.1</span>
</dd><dt><code>timestamps</code></dt><dd>Provides timing information about the volume. Up to four
sub-elements are present,
where <code>atime</code>, <code>btime</code>, <code>ctime</code>
and <code>mtime</code> hold the access, birth, change and
modification time of the volume, where known. The used time
format is <seconds>.<nanoseconds> since the
beginning of the epoch (1 Jan 1970). If nanosecond resolution
is 0 or otherwise unsupported by the host OS or filesystem,
then the nanoseconds part is omitted. This is a readonly
attribute and is ignored when creating a volume.
<span class="since">Since 0.10.0</span>
</dd><dt><code>encryption</code></dt><dd>If present, specifies how the volume is encrypted. See
the <a href="formatstorageencryption.html" shape="rect">Storage Encryption</a> page
for more information.
</dd></dl>
<h3>
<a name="StoragePoolExtents" shape="rect" id="StoragePoolExtents">Device extents</a>
</h3>
<p>
If a storage pool exposes information about its underlying
placement / allocation scheme, the <code>device</code> element
within the <code>source</code> element may contain information
about its available extents. Some pools have a constraint that
a volume must be allocated entirely within a single constraint
(eg disk partition pools). Thus the extent information allows an
application to determine the maximum possible size for a new
volume
</p>
<p>
For storage pools supporting extent information, within each
<code>device</code> element there will be zero or more <code>freeExtent</code>
elements. Each of these elements contains two attributes, <code>start</code>
and <code>end</code> which provide the boundaries of the extent on the
device, measured in bytes. <span class="since">Since 0.4.1</span>
</p>
<h2>
<a name="StorageVol" shape="rect" id="StorageVol">Storage volume XML</a>
</h2>
<p>
A storage volume will generally be either a file or a device
node; <span class="since">since 1.2.0</span>, an optional
output-only attribute <code>type</code> lists the actual type
(file, block, dir, network, or netdir), which is also available
from <code>virStorageVolGetInfo()</code>. The storage volume
XML format is available <span class="since">since 0.4.1</span>
</p>
<h3>
<a name="StorageVolFirst" shape="rect" id="StorageVolFirst">General metadata</a>
</h3>
<pre xml:space="preserve">
<volume type='file'>
<name>sparse.img</name>
<key>/var/lib/xen/images/sparse.img</key>
<allocation>0</allocation>
<capacity unit="T">1</capacity>
...</pre>
<dl><dt><code>name</code></dt><dd>Providing a name for the volume which is unique to the pool.
This is mandatory when defining a volume. <span class="since">Since 0.4.1</span></dd><dt><code>key</code></dt><dd>Providing an identifier for the volume which is globally unique.
This cannot be set when creating a volume: it is always generated.
<span class="since">Since 0.4.1</span></dd><dt><code>allocation</code></dt><dd>Providing the total storage allocation for the volume. This
may be smaller than the logical capacity if the volume is sparsely
allocated. It may also be larger than the logical capacity if the
volume has substantial metadata overhead. This value is in bytes.
If omitted when creating a volume, the volume will be fully
allocated at time of creation. If set to a value smaller than the
capacity, the pool has the <strong>option</strong> of deciding
to sparsely allocate a volume. It does not have to honour requests
for sparse allocation though. Different types of pools may treat
sparse volumes differently. For example, the <code>logical</code>
pool will not automatically expand volume's allocation when it
gets full; the user is responsible for doing that or configuring
dmeventd to do so automatically.<br />
<br />
By default this is specified in bytes, but an optional attribute
<code>unit</code> can be specified to adjust the passed value.
Values can be: 'B' or 'bytes' for bytes, 'KB' (kilobytes,
10<sup>3</sup> or 1000 bytes), 'K' or 'KiB' (kibibytes,
2<sup>10</sup> or 1024 bytes), 'MB' (megabytes, 10<sup>6</sup>
or 1,000,000 bytes), 'M' or 'MiB' (mebibytes, 2<sup>20</sup>
or 1,048,576 bytes), 'GB' (gigabytes, 10<sup>9</sup> or
1,000,000,000 bytes), 'G' or 'GiB' (gibibytes, 2<sup>30</sup>
or 1,073,741,824 bytes), 'TB' (terabytes, 10<sup>12</sup> or
1,000,000,000,000 bytes), 'T' or 'TiB' (tebibytes,
2<sup>40</sup> or 1,099,511,627,776 bytes), 'PB' (petabytes,
10<sup>15</sup> or 1,000,000,000,000,000 bytes), 'P' or 'PiB'
(pebibytes, 2<sup>50</sup> or 1,125,899,906,842,624 bytes),
'EB' (exabytes, 10<sup>18</sup> or 1,000,000,000,000,000,000
bytes), or 'E' or 'EiB' (exbibytes, 2<sup>60</sup> or
1,152,921,504,606,846,976 bytes). <span class="since">Since
0.4.1, multi-character <code>unit</code> since
0.9.11</span></dd><dt><code>capacity</code></dt><dd>Providing the logical capacity for the volume. This value is
in bytes by default, but a <code>unit</code> attribute can be
specified with the same semantics as for <code>allocation</code>
This is compulsory when creating a volume.
<span class="since">Since 0.4.1</span></dd><dt><code>source</code></dt><dd>Provides information about the underlying storage allocation
of the volume. This may not be available for some pool types.
<span class="since">Since 0.4.1</span></dd><dt><code>target</code></dt><dd>Provides information about the representation of the volume
on the local host. <span class="since">Since 0.4.1</span></dd></dl>
<h3>
<a name="StorageVolTarget" shape="rect" id="StorageVolTarget">Target elements</a>
</h3>
<p>
A single <code>target</code> element is contained within the top level
<code>volume</code> element. This tag is used to describe the mapping of
the storage volume into the host filesystem. It can contain the following
child elements:
</p>
<pre xml:space="preserve">
...
<target>
<path>/var/lib/virt/images/sparse.img</path>
<format type='qcow2'/>
<permissions>
<owner>107</owner>
<group>107</group>
<mode>0744</mode>
<label>virt_image_t</label>
</permissions>
<compat>1.1</compat>
<features>
<lazy_refcounts/>
</features>
</target></pre>
<dl><dt><code>path</code></dt><dd>Provides the location at which the volume can be accessed on
the local filesystem, as an absolute path. This is a readonly
attribute, so shouldn't be specified when creating a volume.
<span class="since">Since 0.4.1</span></dd><dt><code>format</code></dt><dd>Provides information about the pool specific volume format.
For disk pools it will provide the partition type. For filesystem
or directory pools it will provide the file format type, eg cow,
qcow, vmdk, raw. If omitted when creating a volume, the pool's
default format will be used. The actual format is specified via
the <code>type</code> attribute. Consult the pool-specific docs for
the list of valid values. <span class="since">Since 0.4.1</span></dd><dt><code>permissions</code></dt><dd>Provides information about the default permissions to use
when creating volumes. This is currently only useful for directory
or filesystem based pools, where the volumes allocated are simple
files. For pools where the volumes are device nodes, the hotplug
scripts determine permissions. It contains 4 child elements. The
<code>mode</code> element contains the octal permission set. The
<code>owner</code> element contains the numeric user ID. The <code>group</code>
element contains the numeric group ID. The <code>label</code> element
contains the MAC (eg SELinux) label string.
<span class="since">Since 0.4.1</span>
</dd><dt><code>compat</code></dt><dd>Specify compatibility level. So far, this is only used for
<code>type='qcow2'</code> volumes. Valid values are <code>0.10</code>
and <code>1.1</code> so far, specifying QEMU version the images should
be compatible with. If the <code>feature</code> element is present,
1.1 is used. If omitted, qemu-img default is used.
<span class="since">Since 1.1.0</span>
</dd><dt><code>features</code></dt><dd>Format-specific features. Only used for <code>qcow2</code> now.
Valid sub-elements are:
<ul><li><code><lazy_refcounts/></code> - allow delayed reference
counter updates. <span class="since">Since 1.1.0</span></li></ul>
</dd></dl>
<h3>
<a name="StorageVolBacking" shape="rect" id="StorageVolBacking">Backing store elements</a>
</h3>
<p>
A single <code>backingStore</code> element is contained within the top level
<code>volume</code> element. This tag is used to describe the optional copy
on write, backing store for the storage volume. It can contain the following
child elements:
</p>
<pre xml:space="preserve">
...
<backingStore>
<path>/var/lib/virt/images/master.img</path>
<format type='raw'/>
<permissions>
<owner>107</owner>
<group>107</group>
<mode>0744</mode>
<label>virt_image_t</label>
</permissions>
</backingStore>
</volume></pre>
<dl><dt><code>path</code></dt><dd>Provides the location at which the backing store can be accessed on
the local filesystem, as an absolute path. If omitted, there is no
backing store for this volume.
<span class="since">Since 0.6.0</span></dd><dt><code>format</code></dt><dd>Provides information about the pool specific backing store format.
For disk pools it will provide the partition type. For filesystem
or directory pools it will provide the file format type, eg cow,
qcow, vmdk, raw. The actual format is specified via the type attribute.
Consult the pool-specific docs for the list of valid
values. Most file formats require a backing store of the same format,
however, the qcow2 format allows a different backing store format.
<span class="since">Since 0.6.0</span></dd><dt><code>permissions</code></dt><dd>Provides information about the permissions of the backing file.
It contains 4 child elements. The
<code>mode</code> element contains the octal permission set. The
<code>owner</code> element contains the numeric user ID. The <code>group</code>
element contains the numeric group ID. The <code>label</code> element
contains the MAC (eg SELinux) label string.
<span class="since">Since 0.6.0</span>
</dd></dl>
<h2>
<a name="examples" shape="rect" id="examples">Example configuration</a>
</h2>
<p>
Here are a couple of examples, for a more complete set demonstrating
every type of storage pool, consult the <a href="storage.html" shape="rect">storage driver page</a>
</p>
<h3>
<a name="exampleFile" shape="rect" id="exampleFile">File based storage pool</a>
</h3>
<pre xml:space="preserve">
<pool type="dir">
<name>virtimages</name>
<target>
<path>/var/lib/virt/images</path>
</target>
</pool></pre>
<h3>
<a name="exampleISCSI" shape="rect" id="exampleISCSI">iSCSI based storage pool</a>
</h3>
<pre xml:space="preserve">
<pool type="iscsi">
<name>virtimages</name>
<source>
<host name="iscsi.example.com"/>
<device path="iqn.2013-06.com.example:iscsi-pool"/>
<auth type='chap' username='myuser'>
<secret usage='libvirtiscsi'/>
</auth>
</source>
<target>
<path>/dev/disk/by-path</path>
</target>
</pool></pre>
<h3>
<a name="exampleVol" shape="rect" id="exampleVol">Storage volume</a>
</h3>
<pre xml:space="preserve">
<volume>
<name>sparse.img</name>
<allocation>0</allocation>
<capacity unit="T">1</capacity>
<target>
<path>/var/lib/virt/images/sparse.img</path>
<permissions>
<owner>107</owner>
<group>107</group>
<mode>0744</mode>
<label>virt_image_t</label>
</permissions>
</target>
</volume></pre>
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