OVF and OVA File Formats

OVF stannds for Open Virtualization Format and OVA stands for Open Virtualization Appliance. Both formats are actually used in VM exporting and importing. You can use the export function to distribute pre-installed software as a virtual appliance, or to distributing template virtual machines to users. You can make the OVF or OVA file available to users who cannot access your vCenter Server inventory.

An OVF is usually made up of several files, as one or several disk images, typically in the widely-used VMDK format and a textual description file in an XML dialect with an .ovf extension. These files must then reside in the same directory for VirtualBox to be able to import them.
Usually this is a small description file (.ovf), the VMs state files (ie it’s disk – *.vhd or *.vmdk) and sometimes a manifest file (.mf).
Classic example is if you download the vCenter Server 5.1 Appliance, it’s a small .ovf file (9.1KB), and 2 disks (system disk – XXGB, data disk – XXMB).

OVF can contain information about the format of a virtual disk image file as well as a description of the virtual hardware that should be emulated to run the OS or application contained on such a disk image.

Alternatively, the above files can be packed together into a single archive file, typically with an .ova extension. (Such archive files use a variant of the TAR archive format and can therefore be unpacked outside of VirtualBox with any utility that can unpack standard TAR files.) 

The OVF and OVA formats offer the following advantages:

  • OVF and OVA files are compressed, allowing for faster downloads.
  • The vSphere Web Client validates an OVF or OVA file before importing it, and ensures that it is compatible with the intended destination server. If the appliance is incompatible with the selected host, it cannot be imported and an error message appears.
  • OVF and OVA can encapsulate multi-tiered applications and more than one virtual machine.


Anup Chhetri

IT system administrator

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