Citrix, Novell make a valid run at VMware ESX virtualization crown

VMware and Microsoft should be taking the competition in the server virtualization market very seriously because open source Xen-based products have definitely matured into viable enterprise-class hypervisor options.

That's what we found in our unique, two-tiered test, in which we pitted three Xen-based virtualization platforms — Citrix Systems', Novell's and Virtual Iron Software's — against each other and against the results of our test of VMware's ESX and Microsoft's Hyper-V.

The winner in our all-Xen test was Citrix's XenServer, which combined solid performance and a strong overall package for those who want to virtualize Windows and Linux systems.

XenServer offered up the highest speeds in our business-transaction tests, even though it did not have a great showing in our I/O performance testing. (See the complete results of our Xen-based hypervisor performance test.) XenServer's management components were flexible and easy to use, despite being a bit buggy. And it's long list of supported guest operating systems adds to its overall enterprise appeal.

Neither Novell's SUSE Xen or Virtual Iron should be ignored, however. We found both have plausible audiences. Novell's Xen is ships as part and parcel of the company's SUSE Linux Enterprise Server (SLES) 10.2 package and Novell's overall support system is highly evolved and very responsive.

Virtual Iron's unique approach — comprising a convenient, server-farm-like approach to virtual machine (VM) guest management — provides an out-of-network administrative link that's potentially more secure than other implementations.

In looking at the hypervisor landscape we've tested so far, VMware's ESX and VirtualCenter combination still is the product to beat because of its wide compatibility list, decent performance and rich management components.

Some background

The open source Xen hypervisor originally supported only Linux machines. Today Xen can represent host hardware to almost any guest that has drivers to support the underlying hardware.

SUSE first bundled Xen in SLES 9.1, that was before Novell acquired SUSE in 2004. Citrix picked up its Xen capabilities when it acquired XenSource in 2007. (Listen to a podcast with Citrix virtualization CTO Simon Crosby.) Both Novell and Citrix still contribute to the Xen project and base their current products on Xen 3.2 code.

The master/slave relationship Virtual Iron establishes between its hypervisor and its guests is a different metaphor for VM hosting. It uses one or more controller servers to manage other servers running hypervisors over a private network.

To assess how these three packages measure up against the non-Xen hypervisors, we asked vendors to submit a base hypervisor package and either built-in or add-on management package roughly equal to the offerings we tested from VMware and Microsoft. Citrix and Virtual Iron complied with the request in full, but Novell would not submit its Orchestrator management application — which has a plug-in module called ZenWorks Virtual Machine Management — for review. With Novell's insistance, we tested SLES 10.2 with is virtualization building blocks but without the add-on management application.

The packages tested in this round were Novell SUSE Xen 3.2 (included with SLES 10.2), Citrix XenServer 5.0 and Virtual Iron 4.4 Extended Enterprise Edition.

The characteristics weighted heavily in this qualitative assessment were hardware and guest operating-system compatibility and the management tools provided to build new VMs, migrate existing VMs, consolidate older server instances onto new virtual ones and control all VMs for day-to-day operation.