25.2. Volumes

Storage pools are divided into storage volumes. Storage volumes are an abstraction of physical partitions, LVM logical volumes, file-based disk images and other storage types handled by libvirt. Storage volumes are presented to virtualized guests as local storage devices regardless of the underlying hardware.

Referencing volumes

To reference a specific volume, three approaches are possible:

The name of the volume and the storage pool

A volume may be referred to by name, along with an identifier for the storage pool it belongs in. On the virsh command line, this takes the form --pool storage_pool volume_name.

For example, a volume named firstimage in the guest_images pool.

# virsh vol-info --pool guest_images
						firstimage
Name:           firstimage
Type:           block
Capacity:       20.00 GB
Allocation:     20.00 GB

virsh #

The full path to the storage on the host system

A volume may also be referred to by its full path on the file system. When using this approach, a pool identifier does not need to be included.

For example, a volume named secondimage.img, visible to the host system as /images/secondimage.img. The image can be referred to as /images/secondimage.img.

# virsh vol-info /images/secondimage.img
Name:           secondimage.img
Type:           file
Capacity:       20.00 GB
Allocation:     136.00 KB

The unique volume key

When a volume is first created in the virtualization system, a unique identifier is generated and assigned to it. The unique identifier is termed the volume key. The format of this volume key varies upon the storage used.

When used with block based storage such as LVM, the volume key may follow this format:

c3pKz4-qPVc-Xf7M-7WNM-WJc8-qSiz-mtvpGn

When used with file based storage, the volume key may instead be a copy of the full path to the volume storage.

/images/secondimage.img

For example, a volume with the volume key of Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr:

# virsh vol-info Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
Name:           firstimage
Type:           block
Capacity:       20.00 GB
Allocation:     20.00 GB

virsh provides commands for converting between a volume name, volume path, or volume key:

vol-name

Returns the volume name when provided with a volume path or volume key.

# virsh vol-name /dev/guest_images/firstimage firstimage
# virsh vol-name Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr

vol-path

Returns the volume path when provided with a volume key, or a storage pool identifier and volume name.

# virsh vol-path Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
/dev/guest_images/firstimage
# virsh vol-path --pool guest_images firstimage
/dev/guest_images/firstimage

The vol-key command

Returns the volume key when provided with a volume path, or a storage pool identifier and volume name.

# virsh vol-key /dev/guest_images/firstimage
Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
# virsh vol-key --pool guest_images firstimage Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr