When adding an image to Glance, you must specify what the virtual machine image’s disk format and container format are. Disk and container formats are configurable on a per-deployment basis. This document intends to establish a global convention for what specific values of disk_format and container_format mean.
The disk format of a virtual machine image is the format of the underlying disk image. Virtual appliance vendors have different formats for laying out the information contained in a virtual machine disk image.
You can set your image’s disk format to one of the following:
This is an unstructured disk image format.
The raw
image format is the simplest one, and is natively supported by
both KVM and Xen hypervisors. You can think of a raw image as being the
bit-equivalent of a block device file, created as if somebody had copied,
say, /dev/sda
to a file using the dd command.
vhd
format. It has support for larger disk sizes
and protection against data corruption during power failures.The AKI/AMI/ARI
format was the initial image format supported by Amazon EC2.
The image consists of three files, each of which has its own specific
disk_format
identifier:
vmlinuz
file.initrd
file.The container format refers to whether the virtual machine image is in a file format that also contains metadata about the actual virtual machine.
Note the following:
Glance does not verify that the container_format
image property
accurately describes the image data payload.
Do not assume that all OpenStack services can handle all the container formats defined by Glance.
Consult the documentation for the service consuming your image to see what container formats the service supports.
You can set your image’s container format to one of the following:
OVF
(Open Virtualization Format) is a packaging format for virtual machines,
defined by the Distributed Management Task Force (DMTF) standards group.
An OVF package contains one or more image files, a .ovf
XML metadata file
that contains information about the virtual machine, and possibly other
files as well.
An OVF package can be distributed in different ways. For example,
it could be distributed as a set of discrete files, or as a tar archive
file with an .ova
(open virtual appliance/application) extension.
The exact format of the compressed file is not specified. It is the responsibility of the consuming service to analyze the data payload and determine the specific compression format. A particular OpenStack service may only support specific formats.
You may assume that any OpenStack service that creates an image with a ‘compressed’ container format will be able to consume that image.
Consult the documentation for the service that will consume your image for details.
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