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.
The top level tag for a storage pool document is 'pool'. It has
a single attribute type, which is one of dir,
fs, netfs, disk,
iscsi, logical, scsi
(all since 0.4.1), mpath
(since 0.7.1), rbd
(since 0.9.13), sheepdog
(since 0.10.0),
gluster (since
1.2.0) or zfs (since
1.2.8). This corresponds to the
storage backend drivers listed further along in this document.
<pool type="iscsi">
<name>virtimages</name>
<uuid>3e3fce45-4f53-4fa7-bb32-11f34168b82b</uuid>
<allocation>10000000</allocation>
<capacity>50000000</capacity>
<available>40000000</available>
...
nameuuidallocationcapacityavailable
A single source element is contained within the top level
pool 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:
...
<source>
<host name="iscsi.example.com"/>
<device path="demo-target"/>
<auth type='chap' username='myname'>
<secret usage='mycluster_myname'/>
</auth>
<vendor name="Acme"/>
<product name="model"/>
</source>
...
...
<source>
<adapter type='scsi_host' name='scsi_host1'/>
</source>
...
...
<source>
<adapter type='scsi_host'>
<parentaddr unique_id='1'>
<address domain='0x0000' bus='0x00' slot='0x1f' addr='0x2'/>
</parentaddr>
</adapter>
</source>
...
...
<source>
<adapter type='fc_host' parent='scsi_host5' wwnn='20000000c9831b4b' wwpn='10000000c9831b4b'/>
</source>
...
devicefs, logical, disk,
iscsi, zfs).
May be repeated multiple times depending on backend driver. Contains
a single attribute path which is the fully qualified
path to the block device node. Since 0.4.1dirdir), or optionally to select a subdirectory
within a pool that resembles a filesystem (pool
type gluster). May
only occur once. Contains a single attribute path
which is the fully qualified path to the backing directory.
Since 0.4.1adapterscsi). May only occur once.
namevirsh nodedev-list
scsi_host command followed by a combination of
lspci and virsh nodedev-dumpxml
scsi_hostN commands to find the scsi_hostN
to be used. Since 0.6.2
It is further recommended to utilize the
parentaddr element since it's possible to have
the path to which the scsi_hostN uses change between system
reboots. Since 1.2.7
typename attribute is
specified, then it defaults to "scsi_host". To keep backwards
compatibility, this attribute is optional only for the
"scsi_host" adapter, but is mandatory for the "fc_host" adapter.
Since 1.0.5
A "fc_host" capable scsi_hostN can be determined by using
virsh nodedev-list --cap fc_host.
Since 1.2.8
Note: Regardless of whether a "scsi_host" adapter type is defined
using a name or a parentaddr, it
should refer to a real scsi_host adapter as found through a
virsh nodedev-list scsi_host and virsh
nodedev-dumpxml scsi_hostN on one of the scsi_host's
displayed. It should not refer to a "fc_host" capable scsi_hostN
nor should it refer to the vHBA created for some "fc_host"
adapter. For a vHBA the nodedev-dumpxml
output parent setting will be the "fc_host" capable scsi_hostN
value. Additionally, do not refer to an iSCSI scsi_hostN for the
"scsi_host" source. An iSCSI scsi_hostN's
nodedev-dumpxml output parent field is generally
"computer". This is a libvirt created parent value indicating
no parent was defined for the node device.
wwnn and wwpnwwnn) and "World Wide
Port Name" (wwpn) 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. Use the command 'virsh nodedev-dumpxml' to determine
how to set the values for the wwnn/wwpn of a (v)HBA. The wwnn and
wwpn have very specific numerical format requirements based on the
hypervisor being used, thus care should be taken if you decide to
generate your own to follow the standards; otherwise, the pool
will fail to start with an opaque error message indicating failure
to write to the vport_create file during vport create/delete due
to "No such file or directory".
Since 1.0.4
parentmanagedparentaddrname attribute to more uniquely identify the
SCSI host. Using a combination of the unique_id
attribute and the address element to formulate
a PCI address, a search will be performed of the
/sys/class/scsi_host/hostNN links for a
matching PCI address with a matching unique_id
value in the /sys/class/scsi_host/hostNN/unique_id
file. The value in the "unique_id" file will be unique enough
for the specific PCI address. The hostNN will be
used by libvirt as the basis to define which SCSI host is to
be used for the currently booted system.
Since 1.2.7
addressdomain (a 2-byte hex integer, not currently used
by qemu), bus (a hex value between 0 and 0xff,
inclusive), slot (a hex value between 0x0 and
0x1f, inclusive), and function (a value between
0 and 7, inclusive). The PCI address can be determined by
listing the /sys/bus/pci/devices and the
/sys/class/scsi_host directories in order to
find the expected scsi_host device. The address will be
provided in a format such as "0000:00:1f:2" which can be
used to generate the expected PCI address
"domain='0x0000' bus='0x00' slot='0x1f' function='0x0'".
Optionally, using the combination of the commands 'virsh
nodedev-list scsi_host' and 'virsh nodedev-dumpxml' for a
specific list entry and converting the resulting
path element as the basis to formulate the
correctly formatted PCI address.
unique_idparentaddr attribute used to determine
which of the scsi_host adapters for the provided PCI address
should be used. The value is determine by contents of the
unique_id file for the specific scsi_host adapter.
For a PCI address of "0000:00:1f:2", the unique identifer files
can be found using the command
find -H /sys/class/scsi_host/host*/unique_id |
xargs grep '[0-9]'. Optionally, the
virsh nodedev-dumpxml scsi_hostN' of a
specific scsi_hostN list entry will list the
unique_id value.
hostnetfs, iscsi,
rbd, sheepdog, gluster). Will be
used in combination with a directory
or device element. Contains an attribute name
which is the hostname or IP address of the server. May optionally
contain a port attribute for the protocol specific
port number. Since 0.4.1authauth element provides the
authentication credentials needed to access the source by the
setting of the type attribute (pool
types iscsi, rbd). The type
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
username identifies the username to use during
authentication as well as a sub-element secret with
a mandatory attribute type, to tie back to a
libvirt secret object 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 secret element requires either a uuid
attribute with the UUID of the secret object or a usage
attribute matching the key that was specified in the
secret object. Since 0.9.7 for "ceph" and
1.1.1 for "chap"
namelogical, rbd,
sheepdog, gluster). Contains a
string identifier.
Since 0.4.5formatfs, netfs, disk,
logical). This
contains a single attribute type 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. Since 0.4.1vendorname whose value is backend
specific. Since 0.8.4productname whose value
is backend specific. Since 0.8.4
A single target element is contained within the top level
pool element for some types of pools (pool
types dir, fs, netfs,
logical, disk, iscsi,
scsi, mpath). This tag is used to
describe the mapping of
the storage pool into the host filesystem. It can contain the following
child elements:
...
<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>
path/dev/ 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 /dev/disk/by-{path,id,uuid,label locations.
Since 0.4.1
permissionsmode element contains the octal permission set. The
owner element contains the numeric user ID. The group
element contains the numeric group ID. The label element
contains the MAC (eg SELinux) label string.
Since 0.4.1
timestampsatime, btime, ctime
and mtime 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.
Since 0.10.0
encryption
If a storage pool exposes information about its underlying
placement / allocation scheme, the device element
within the source 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
For storage pools supporting extent information, within each
device element there will be zero or more freeExtent
elements. Each of these elements contains two attributes, start
and end which provide the boundaries of the extent on the
device, measured in bytes. Since 0.4.1
A storage volume will generally be either a file or a device
node; since 1.2.0, an optional
output-only attribute type lists the actual type
(file, block, dir, network, or netdir), which is also available
from virStorageVolGetInfo(). The storage volume
XML format is available since 0.4.1
<volume type='file'>
<name>sparse.img</name>
<key>/var/lib/xen/images/sparse.img</key>
<allocation>0</allocation>
<capacity unit="T">1</capacity>
...
namekeyallocationlogical
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.unit can be specified to adjust the passed value.
Values can be: 'B' or 'bytes' for bytes, 'KB' (kilobytes,
103 or 1000 bytes), 'K' or 'KiB' (kibibytes,
210 or 1024 bytes), 'MB' (megabytes, 106
or 1,000,000 bytes), 'M' or 'MiB' (mebibytes, 220
or 1,048,576 bytes), 'GB' (gigabytes, 109 or
1,000,000,000 bytes), 'G' or 'GiB' (gibibytes, 230
or 1,073,741,824 bytes), 'TB' (terabytes, 1012 or
1,000,000,000,000 bytes), 'T' or 'TiB' (tebibytes,
240 or 1,099,511,627,776 bytes), 'PB' (petabytes,
1015 or 1,000,000,000,000,000 bytes), 'P' or 'PiB'
(pebibytes, 250 or 1,125,899,906,842,624 bytes),
'EB' (exabytes, 1018 or 1,000,000,000,000,000,000
bytes), or 'E' or 'EiB' (exbibytes, 260 or
1,152,921,504,606,846,976 bytes). Since
0.4.1, multi-character unit since
0.9.11capacityunit attribute can be
specified with the same semantics as for allocation
This is compulsory when creating a volume.
Since 0.4.1sourcetarget
A single target element is contained within the top level
volume element. This tag is used to describe the mapping of
the storage volume into the host filesystem. It can contain the following
child elements:
...
<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>
<nocow/>
<features>
<lazy_refcounts/>
</features>
</target>
pathformattype attribute. Consult the
storage driver page for the list of valid
volume format type values for each specific pool. The
format will be ignored on input for pools without a
volume format type value and the default pool format will be used.
Since 0.4.1permissionsmode element contains the octal permission set. The
owner element contains the numeric user ID. The group
element contains the numeric group ID. The label element
contains the MAC (eg SELinux) label string.
Since 0.4.1
compattype='qcow2' volumes. Valid values are 0.10
and 1.1 so far, specifying QEMU version the images should
be compatible with. If the feature element is present,
1.1 is used. If omitted, qemu-img default is used.
Since 1.1.0
nocowfeaturesqcow2 now.
Valid sub-elements are:
<lazy_refcounts/> - allow delayed reference
counter updates. Since 1.1.0
A single backingStore element is contained within the top level
volume 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:
...
<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>
pathformatpermissionsmode element contains the octal permission set. The
owner element contains the numeric user ID. The group
element contains the numeric group ID. The label element
contains the MAC (eg SELinux) label string.
Since 0.6.0
Here are a couple of examples, for a more complete set demonstrating every type of storage pool, consult the storage driver page
<pool type="dir">
<name>virtimages</name>
<target>
<path>/var/lib/virt/images</path>
</target>
</pool>
<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>
<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>