Commit b3e3813e authored by Agata Murawska's avatar Agata Murawska Committed by Iustin Pop
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Initial design doc for OVF support

Signed-off-by: default avatarAgata Murawska <>
[ fixed formatting issues]
Signed-off-by: default avatarIustin Pop <>
Reviewed-by: default avatarIustin Pop <>
Reviewed-by: default avatarMichael Hanselmann <>
parent d6f46b6a
......@@ -12,6 +12,7 @@ Design document drafts
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Ganeti Instance Import/Export using Open Virtualization Format
Open Virtualization Format is an open standard for packaging
information regarding virtual machines. It is used, among other, by
VMWare, VirtualBox and XenServer. OVF allows users to migrate between
virtualization software without the need of reconfiguring hardware,
network or operating system.
Currently, exporting instance in Ganeti results with a configuration
file that is readable only for Ganeti. It disallows the users to
change the platform they use without loosing all the machine's
configuration. Import function in Ganeti is also currently limited to
the previously prepared instances.
Implementation of OVF support allows users to migrate to Ganeti from
other platforms, thus potentially increasing the usage. It also
enables virtual machine end-users to create their own machines
(e.g. in VirtualBox or SUSE Studio) and then add them to Ganeti
cluster, thus providing better personalization.
Open Virtualization Format description
According to the DMTF document introducing the standard: "The Open
Virtualization Format (OVF) Specification describes an open, secure,
portable, efficient and extensible format for the packaging and
distribution of software to be run in virtual machines." OVF supports
both single and multiple- configurations of VMs in one package, is
host- and virtualization platform-independent and optimized for
distribution (e.g. by allowing usage of public key infrastructure and
providing tools for management of basic software licensing).
There are no limitations regarding hard drive images used, as long as
the description is provided. Any hardware described in a proper
i.e. CIM - Common Information Model) format is accepted, although
there is no guarantee that every virtualization software will support
all types of hardware.
OVF package should contain one file with .ovf extension, which is an
XML file specifying the following (per virtual machine):
- virtual disks
- network description
- list of virtual hardware
- operating system, if any
Each of the elements in .ovf file may, if desired, contain a
human-readable description to every piece of information given.
Additionally, the package may have some disk image files and other
additional resources (e.g. ISO images).
Supported disk formats
Although OVF is claimed to support 'any disk format', what we are
interested in is which of the formats are supported by VM managers
that currently use OVF.
- VMWare: ``.vmdk`` (which comes in at least 3 different flavours:
``sparse``, ``compressed`` and ``streamOptimized``)
- VirtualBox: ``.vdi`` (VirtualBox's format), ``.vmdk``, ``.vhd``
(Microsoft and XenServer); export disk format is always ``.vmdk``
- XenServer: ``.vmdk``, ``.vhd``; export disk format is always
- Red Hat Enterprise Virtualization: ``.raw`` (raw disk format),
``.cow`` (qemu's ``QCOW2``)
- other: AbiCloud, OpenNode Cloud, SUSE Studio, Morfeo Claudia,
In our implementation of the OVF we plan to allow a choice between
raw, cow and vmdk disk formats for both import and export. The
justification is the following:
- Raw format is supported as it is the main format of disk images used
in Ganeti, thus it is effortless to provide support for this format
- Cow is used in Qemu, [TODO: ..why do we support it, again? That is,
if we do?]
- Vmdk is most commonly supported in virtualization software, it also
has the advantage of producing relatively small disk images, which
is extremely important advantage when moving instances.
The conversion between RAW and the other formats will be done using
qemu-img, which transforms, among other, raw disk images to monolithic
sparse vmdk images.
Planned limitations
The limitations regarding import of the OVF instances generated
outside Ganeti will be (in general) the same, as limitations for
Ganeti itself. The desired behavior in case of encountering
unsupported element will be to ignore this element's tag and inform
the user on console output, if possible - without interruption of the
import process.
There are no limitations regarding support for multiple files in
package or packing the ovf package into one OVA (Open Virtual
Appliance) file. As for certificates and licenses in the package,
their support will be under discussion after completion of the basic
features implementation.
Multiple Virtual Systems
At first only singular instances (i.e. VirtualSystem, not
VirtualSystemCollection) will be supported. In the future multi-tiered
appliances containing whole nodes (or even clusters) are considered an
As mentioned, Ganeti will allow exporting only ``raw``, ``cow`` and
``vmdk`` formats. As for import, we will support all that
``qemu-img`` can convert to raw format. At this point this means
``raw``, ``cow``, ``qcow``, ``qcow2``, ``vmdk`` and ``cloop``. We do
not plan for now to support ``vdi`` or ``vhd``.
We support compression both for import and export - for export this
will use ovftools with chosen level of compression. There is also a
possibility to provide virtual disk in chunks of equal size.
When no ``ovf:format`` tag is provided during import, we assume that
the disk is to be created on import and proceed accordingly.
There are no known limitations regarding network support.
Operating Systems
Implementation details
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