Configure Compute backing storageBacking Storage is the storage used to provide
the expanded operating system image, and any ephemeral storage.
Inside the virtual machine, this is normally presented as two
virtual hard disks (for example, /dev/vda and /dev/vdb respectively).
However, inside OpenStack, this can be derived from one of three
methods: LVM, QCOW or RAW, chosen using the
libvirt_images_type option in nova.conf
on the compute node.QCOW is the default backing store. It uses a copy-on-write philosophy to
delay allocation of storage until it is actually needed. This means that the
space required for the backing of an image can be significantly less on the real
disk than what seems available in the virtual machine operating system.
RAW creates files without any sort of file formatting, effectively creating
files with the plain binary one would normally see on a real disks. This can
increase performance, but means that the entire size of the virtual disk is
reserved on the physical disk.
Local LVM volumes
can also be used.
Set libvirt_images_volume_group=nova_local where nova_local is the name
of the LVM group you have created.