Virtualisation vendors are fighting to stop the take-up of the technology being thwarted by a war on standards, such as the Blu-ray versus HD-DVD battle, which bedevilled the storage media debate. In particular, vendors are fighting to avoid a conflict over the adoption of virtual appliances.

Such appliances are software bundles containing an operating system and application that have been pre-configured and tuned to run in a virtualised environment. The idea is to ease and speed up deployment of new virtualised applications, but that's contingent on the virtual appliances being able to work with various virtualisation technologies, such as VMware's ESX Server, Citrix Systems' XenServer and Microsoft's new Hyper-V software.

Those three vendors, along with IBM, Hewlett-Packard and Dell, have been working since last year with Distributed Management Task Force, to create an interoperability specification for virtual machines. And they're now far enough along on the specification, called the Open Virtual Machine Format - or OVF, for short - to build tools that conform to it.

Citrix, which bought its way into the server virtualisation market by acquiring XenSource last year, has announced that it plans to offer tools for creating virtual appliances that can run on multiple virtualisation hypervisors, whether they're from Citrix itself or VMware, Microsoft and other vendors.

The new tools, which are being developed under an initiative called Project Kensho, are aimed at users as well as independent software vendors (ISVs) and are scheduled for release in a technical preview during the current quarter.

Simon Crosby, chief technology office for Citrix's virtualization and management division, said the OVF specification is critical to the adoption of virtual appliances. If the virtualisation market were to bifurcate around different formats, "it really ruins a lot of the benefits of virtualisation," Crosby said. He added that in addition to the obvious benefits for ISVs, enterprises could use OVF to make their internally developed applications platform-independent.

Chris Wolf, an analyst at Burton Group, said that OVF Version 1.0 is primarily a specification for distributing virtual machines and importing them into customer environments, and that he thinks the specification has some ways to go before it becomes really useful. For instance, the spec needs more development to enable users to manage the appliances in a heterogeneous environment, Wolf said. But he added that he thinks the vendors and the DMTF are on the path to accomplish that in later releases of OVF.

As the dominant vendor in the virtualisation market, VMware has the most to lose by backing an interoperability specification. But Wolf sees VMware's support for OVF as being linked to its desire to get the investment it has made in management tools to pay off.

Virtual appliances are still limited in use, and Wolf said that Microsoft, for one, is heading down a different path with its support for streaming applications to the desktop.

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