Comparing VMware ESX, VMware Server, Microsoft Virtual Server, Xen and XenEnterprise: Technical spec

In this series   - Choosing the right server virtualization solution part one, introduction   - Choosing the right server virtualization solution part two, technical specifications   - Choosing the right server virtualization solution part three, management   - Choosing the right server virtualization solution part four, additional features

During evaluations of server virtualization platforms, focusing on product features alone isn't such a good idea. A product is only as great as the stuff that comes with it. In part one of this four-part series, I discussed the criteria for our comparisons and looked at administrative features. Now, I'll continue the platform comparisons with an overview of technical specifications and support.

Technical Specifications

Let's compare the virtualization options -- VMware ESX Server 2.5.3, VMware Server, Microsoft Virtual Server 2005, Xen 3.0 and XenEnterprise -- in terms of seven technical support criteria.

Host / Control OS
Some VMMs require a separate host OS or control OS.

VMware ESX 2.5.3 and XenEnterprise get a point each for providing a seamless installation without needing to separately configure a host or control OS. VMware Server, Microsoft Virtual Server 2005 R2 and Xen 3.0 require configuring a host OS or control OS separate from the VMM configuration, and for this reason they lose a point.

Winner(s): VMware ESX 2.5.3, XenEnterprise

Loser(s): VMware Server, Microsoft Virtual Server 2005 R2, Xen 3.0

CPU support
Here, we look at the number of CPUs supported by the VMM.

Wow, VMware really comes out behind here. Microsoft for the win.

Winner(s): Microsoft Virtual Server 2005 R2

Loser(s): VMware ESX Server 2.5.3, VMware Server

System RAM support
Now we'll look at the amount of RAM supported by the VMM.

Xen 3.0 and XenEnterprise support Intel's Physical Address Extension (PAE) that allows up to 64GB of RAM, but currently Xen only supports 16GB of RAM. Until Xen supports the allowed 64GB, the other VMM solutions can tout four times the amount of supported system RAM.

Winner(s): VMware ESX Server 2.5.3, VMware Server, Microsoft Virtual Server 2005 R2

Loser(s): Xen 3.0, XenEnterprise

Hardware compatibility
This next comparison looks at the level and scope of the hardware on which the VMM will function.

The usual heavyweight falls short here. ESX relies on vendor-supplied drivers to support hardware, while the rest of the VMMs support an extremely broad range of hardware devices.

Winner(s): VMware Server, Microsoft Virtual Server 2005 R2, Xen 3.0, XenEnterprise

Loser(s): VMware ESX Server 2.5.3

Virtual SMP support
This section takes a look at whether or not the VMM supports presenting the VMs two or more processors.

There are no winners and losers, but if there were, Microsoft Virtual Server 2005 R2 would have a huge fluorescent green "L" painted on its forehead. Xen 3.0 and XenEnterprise are the clear winners with support for presenting VMs with up to 32 processors.

Winner(s): Xen 3.0, XenEnterprise

Loser(s): Microsoft Virtual Server 2005 R2

VMs per CPU core
How many VMs does each need to run per CPU core?

VMware is the only vendor that comes out and specifies the number of VMs that can run per CPU core. They win for their recommendation, but it is just that, a recommendation. The number of VMs per CPU core does depend heavily on overall usage of the host server. For that reason, Microsoft and Xen do not lose points for not giving their own suggestion.

Winner(s): VMware ESX Server 2.5.3, VMware Server

Loser(s): --

Virtualization mode
What's the type of virtualization being implemented with each option?

Xen has led the paravirtualization revolution, and the speed benefits are tremendous. With Intel VT, Xen can also use HVM to virtualize Windows guests as well. We'll see what the future holds for the rest of the bunch, but for now Xen takes the cake.

Winner(s): Xen 3.0, XenEnterprise

Loser(s): VMware ESX Server 2.5.3, VMware Server, Microsoft Virtual Server 2005 R2

Support

Let's now turn our attention to the support available for each major virtualization option.

Vendor support
Does each vendor offer an official support channel for the product?

VMware ESX Server 2.5.3 and VMware Server win this round, simply by virtue of having a more established presence and better being able to provide product support. The Xen products do not lose points because there is vendor support, but they do not win points either because they have not been in the game long enough to get a a sense of the quality of their support.

Microsoft seems to be following in the trend of Terminal Services when it comes to offering official support for their Virtual Server platform. Microsoft Premier Support Services (PSS) rolls Terminal Services into their Directory Support team. I have personally been involved in problem resolutions that have taken longer than a month and a half to fix because Microsoft cannot get a hold of anyone that knows Terminal Services well enough to help me figure out the problem. I fear that their Virtual Server platform could suffer the same fate if more attention is not paid to it.

Winner(s): VMware ESX Server 2.5.3, VMware Server

Loser(s): Microsoft Virtual Server 2005 R2

Community support
Now we'll look at whether or not there is community/grass-roots support for the product.

While all of the VMMs do enjoy community support, ESX and Xen win because of the sheer number of their partners they have and the zealous grass-roots followings they command. Microsoft's Virtual Server products have traditionally not had the type of overwhelming community support that VMware has enjoyed, or Xen is starting to enjoy.

Winner(s): VMware ESX Server 2.5.3, Xen 3.0, XenEnterprise

Loser(s): Microsoft Virtual Server 2005 R2

Third-party support (consulting and development)
This table examines whether or not there is third-party consultation support as well as third-party development for the product.

VMware ESX Server 2.5.3 and Xen win yet again. This is due in large part to their loyal followings.

Winner(s): VMware ESX Server 2.5.3, Xen 3.0, XenEnterprise

Loser(s): Microsoft Virtual Server 2005 R2

This concludes our look at the technical specifications and support offered by each vendor. Read part three to find out about management and high availability.