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11.2. 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 guest virtual machines 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
--poolstorage_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 physical machine 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 physical machine 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
