Red Hat has rejected XenSource's virtualisation technology as not being ready for enterprise use, according to reports.

That's despite Novell's shipment of the same product with its recently released SuSE Linux Enterprise Server 10 OS.

The technology, dubbed Xen, is a hypervisor-style, Linux-only virtualisation system designed to allow re-use of some elements of the open source OS kernel by virtual machines. It permits better performance and use of resources.

Following the expenditure of millions testing Xen, Red Hat decided it was not yet a stable enough platform on which to base an enterprise's mission-critical systems. Instead, the company may wait for Xen to improve and build it into the next version of Red Hat Enterprise Linux server, due in December.

One analyst, Gordon Haff of Illuminata, reckoned that Novell was able to ship because part of the Xen installer only works with SuSE. He added that the performance profiler was also not yet ready, while the system was not yet secure enough.

His overall take was that: "Xen's current state need not reflect its future prospects. New technologies take time to mature. But headlines and press releases about Xen having arrived notwithstanding, make no mistake about it. This is an experimental product. Kick the tyres if you must but stay off the highway."

At one point, it was looking as if Xen would migrate into the Linux kernel and become a standard part of the system. IBM has already committed to it.

However, questions were raised following XenSource's recent agreement with Microsoft. The agreement allowed a para-virtualised Windows to inter-operate with Xen, and significantly add to Xen's appeal by making Windows Server virtualisation able to run open source Xen-based guest operating systems.

The deal was promptly slated by virtualisation market leader VMware, which called it a "one-way street," and accused XenSource of betraying its open source roots.

VMware said XenSource would be optimising Microsoft code to run on the Xen hypervisor while not allowing Microsoft-XenSource developed code to be used by the open source community.

Brian Byun, VMware's VP of products and alliances, pointed out in his blog that the deal is "a one-way street that favours Microsoft and Windows running Linux. The arrangement will allow Linux to run on future Microsoft hypervisors through translated calls to the hypervisor when Windows is controlling the hardware, but not the other way around. That means there is no mention of Longhorn optimisations or 'enlightenments' being ported to Xen or licensed to XenSource to enable a Xen hypervisor to run full optimisations with Longhorn OS."

So XenSource's Microsoft deal plus its alleged technological failings might result in it being discounted as the virtualisation system of choice for the Linux kernel. Instead, SWsoft, which makes Virtuozzo, could well supplant it.