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 .vhd
  • Red Hat Enterprise Virtualization: .raw (raw disk format), .cow (qemu’s QCOW2)
  • other: AbiCloud, OpenNode Cloud, SUSE Studio, Morfeo Claudia, OpenStack

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.

Import and export - the closer look

This section contains an overview of how different parts of Ganeti’s export info are included in .ovf configuration file. It also explains how import is designed to work with incomplete information.

Ganeti’s backup format vs OVF

The basic structure of Ganeti .ovf file is the following:



Tags with gnt: prefix are Ganeti-specific and are not a part of OVF standard.

Whereas Ganeti’s export info is of the following form, => showing where will the data be in OVF format:

    disk0_dump = filename     => References
    disk0_ivname = name       => ignored
    disk0_size = size_in_mb   => DiskSection
    disk_count = number       => ignored
    disk_template = disk_type => References
    hypervisor = hyp-name     => gnt:HypervisorSection
    name = inst-name          => Name in VirtualSystem
    nic0_ip = ip              => Item in VirtualHardwareSection
    nic0_link = link          => Item in VirtualHardwareSection
    nic0_mac = mac            => Item in VirtualHardwareSection
    nic0_mode = mode          => Network in NetworkSection
    nic_count = number        => ignored
    tags                      => gnt:Tags

    auto_balanced             => gnt:AutoBalance
    memory = mem_in_mb        => Item in VirtualHardwareSection
    vcpus = number            => Item in VirtualHardwareSection

    compression               => DiskSection
    os                        => OperatingSystemSection
    source                    => ignored
    timestamp                 => ignored
    version                   => gnt:VersionId

[os]                          => gnt:OSParameters

[hypervisor]                  => gnt:HypervisorParameters

In case of multiple networks/disks used by an instance, they will all be saved in appropriate sections as specified above for the first network/disk.

Import from other virtualization software

In case of importing to Ganeti OVF package generated in other software, e.g. VirtualBox, some fields required for Ganeti to properly handle import may be missing. Most often it will happen that such OVF package will lack the gnt:GanetiSection.

If this happens, the tool will simply ask for all the necessary information or otherwise you can specify all the missing parameters in the command line. For the latter, please refer to [TODO: reference to command line options]

Export to other virtualization software

When exporting to other virtualization software, you may notice that there is a section gnt:GanetiSection, containing Ganeti-specific information. This may on rare cases cause trouble in importing your instance. If that is the case please do one of the two:

1. Export from Ganeti to OVF with --external option - this will cause to skip the non-standard information.

2. Manually remove the gnt:GanetiSection from the .ovf file. You will also have to recompute sha1 sum (sha1sum command) and update your .mf file with new value.


Manual change option is only recommended when you have exported your instance with -format option other that raw or selected --compress. It saves you the time of converting or compressing the disk image.

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 option.


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 plan to support compression both for import and export - in tar.gz format. 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