One of the best things for innovation is competition. With competition we get vendors competing for our votes ($$$) by adding new and better features. For example, in the virtualization market, there are several major players. vmware, Citrix (Xen), Oracle (VirtualBox), and others are continuously and aggressively releasing new versions of their software.
The challenge with having so much compatibility though is compatibility of virtual machine images. If I have my favorite build on one virtualization solution, but want to check out another virtualization solution, I typically have to reinstall, because the virtual disk images and virtual machine configuration parameters are not compatible. What information do these virtual disk images contain besides the operating system and applications of the virtual machine? The image must also tell the virtual machine manager (hypervisor / host) virtualization information on the processors, disk drive parameters, and network interface card(s). See my article for more information on these elements within a larger article I wrote on running Windows and Linux on Mac computers..
Enter Open Virtualization Format
Open Virtualization Format (OVF) addresses this issue by creating an open format for virtualization developers. OVF was developed by the Distributed Management Task Force, Inc., and the specification is currently in version 1.1.0.
OVF isn't talked about much (it's true value is for large migrations of virtual machines), but most of the vendors support the format. (I'll update links here as time permits.) There are two modes of operations for hypervisors: direct support of OVF or conversion of OVF to the product's native format.
Besides the interoperability the format creates, OVF also supports multiple virtual machines in the same OVF repository. What value does this have? This makes it easier on vendors to create virtual appliance solutions that require multiple machines. For example, consider a load balancing solution...the vendor could provide an OVF repository that contains images for both of the virtual machines that make up the load balancer.
This section will be updated from time to time, so if you would like to see something added to this section, please drop me a line.
VirtualBox 4.0 supports OVF through import and export functions in the Oracle VM VirtualBox manager. The project also maintains a few appliances in the OVF.
vmware provides the ovf tool for importing and exporting ovf images.
Citrix provides it's tool XenConvert to convert virtual machine images to it's native format. The tool will also convert physical machines to the Xen format.
1.1 1/16/11 - Added Other Sources Section
1.0 1/13/10 - Original