Virtualization: Xen vs. Microsoft vs. VMware

Tuesday Feb 13th 2007 by David Strom
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A guide to choosing the best virtual server, looking at factors like host hardware and guest OSes. Plus: a chart that compares offerings by Xen, VMware, and Microsoft.

Also see: VMware vs Microsoft vs Xen: 2009

Here's the updated 2008 version of this article: Virtual Servers Update: VMware vs. Microsoft vs. Xen

Server virtualization has become a great tool for the data center, helped by the leading virtual server software vendors literally giving away their product. And as more IT shops consolidate their servers using virtual machines (VMs), they find an active marketplace and plenty of choices for how to implement the concept.

Adoption of server virtualization is accelerating. According to a Forrester Research, survey 51 percent of enterprises are now using or piloting the technology.

It’s a powerful notion: take a single computer (a dual core or multi-processor CPU is best), and divvy it up into separate "virtual" machines with their own memory, virtual hardware and drive images, and other resources. It isn't new: IBM has been doing this on its mainframes for more than 30 years, and we've had blade servers for the past five years too. But what is new is that the power of VM can be delivered to the PC platform, and there is a more compelling argument now that Microsoft’s Virtual PC and EMC's VMware have free versions, along with pre-configured VMs to make setup even easier. EMC offers this page with dozens of different "virtual appliances" that have already been configured for popular Web, database, and other applications servers. Just copy them and you’re ready to run something that could have taken hours or days to setup.

Microsoft even offers a virtual disk image that contains XP with Service Pack 2 and IE 6 for those shops that need to run IE 6 and 7 side-by-side. They also offer pre-built images of Exchange, SQL Server, and Windows Server 2003.

The idea is to run multiple operating systems and applications on the same box, making it easier to provision a new server and make more productive use of this hardware, just like our mainframe antecedents used to do in the 1980s. But unlike the mainframe era, having multiple VMs means IT shops can cut the cost of software development and simplify configuration as they deploy new servers. By eliminating the need for particular peripherals or supporting a particular graphics or network card, a VM set-up cuts the time to configure a new server. And now that there is more power available on the PC platform, it makes a case for more consolidation.

"Two years ago, it wouldn't have been possible to handle so much workload in a datacenter. Now we can, thanks to this new virtualization software," says Rene Wienholtz, the CTO of a Germany Web hosting provider called Strato that has deployed these technologies.

The key to successfully using VMs is to make them as cookie-cutter as possible, so that they can be quickly setup and cloned as new virtual servers are needed for the datacenter.

Comparing the alternatives

There are three major VM vendors currently, with others such as VirtualIron.com coming on strong too. EMC's VMware has been around the longest and has the most complex product line, with both free and paid versions. Microsoft purchased its line of virtual servers from Connectix and now offers the product for free, and Xensource.com has an open-source alternative that has both free and paid versions.

Next page: Five tips for choosing virtual servers. Plus: a comparison chart for Xen, Microsoft, and VMware.

Before you choose your VM server vendor, here are some questions to ask to qualify the kind of product that will serve your needs best:

1) What host hardware and operating system will you want to run?

Each VM server product hosts its virtual machines in different ways. Some, such as the free VMware Server and Microsoft's Virtual Server, run on top of ordinary Windows Server machines. There is a difference, however: Microsoft requires a lot more than just the OS to run its virtual server product. you have to run the latest SPs and IIS and Active Directory and use IE. VMware needs just the basic OS. (More on that in a moment.)

VMware Server also runs on numerous Linux distributions, and Microsoft's supports testing but not production use on XP Professional. Others, such as the paid VMware versions and Xensource, run on the "bare metal" of a PC – meaning that no OS is needed, and they install their own miniature OS to operate the various VMs. These usually support the more recently higher-performance CPUs, but finding the right drivers to run these bare metal OSes may be an issue. It depends on what host OS you’re comfortable using in your enterprise and under what conditions.

2) What guest OSes do you plan on using?

Each VM product can run just about any "guest" OS but some are better tuned and pre-configured for particular OSes. VMware has the widest support for many different Windows, Linux, and Unix OSes. Microsoft is of course more focused on their own Windows versions, and Xen supports some Windows and Linux versions and is adding more.

3) How many VM hosts do you plan on operating and how will you manage them?

Each virtual server solution has slightly different management tools and consoles to connect with the VMs that it is running. Microsoft is the most closely tied to Windows and its own software such as Internet Information Server. The management tool runs under IE v6 or later and you can view the console of each VM inside the browser frame. They have another tool that is in beta (expected in the latter part of 2007) called System Center VM manager that will require Active Directory running on the host Windows Server 2003 machine. Xensource's Administrator Console runs on both Linux and Windows.

4) How familiar are you with VM concepts and how important is support?

Part of operating VMs is having a solid base of support behind the products. VMware has been around the longest and has the best-developed reseller and support channel. While Xensource is open source, the community is still pretty new and getting started. If you have subscriptions to the various Microsoft TechNet and MSDN offerings you will have the resources to make use of its product.

5) What is the difference between free and paid products?

Each of the three major vendors offers free products: VMware Server, Microsoft's Virtual Server, and XenExpress. VMware offers three different paid versions of its Infrastructure line – Starter, Standard, and Enterprise, with corresponding price increases. All three include the basic ESX software that runs the VMs, along with management tools. The more expensive versions include support for server clustering and other high-availability options.

Xensource has two paid versions, XenServer and XenEnterprise. The former is licensed at $99 per year while the latter can be either licensed at $488 per year or purchased for a single fee of $750, so obviously for longer periods the purchase is the most cost-effective. The table below summarizes the various options for these three vendors.

Table: Virtual Server product comparison

 

VMware/EMC

Microsoft

Xen

URL

Vmware.com

Microsoft.com/virtual server

Xensource.com

Free server product

VMware Server

Virtual Server 2005 R2

XenExpress

Paid server products

Infrstructure v3 (Starter, Standard, and Enterprise)

None

XenServer and Enterprise

Pricing range paid product

$1000 - $5750 (two CPU versions)

Free

Server : $99/yr Enterprise: $750

Host OS (if any)

Server:Windows Server 2003, various Linux

Infra v3:bare metal

Windows Server 2003 SP1, XP Pro SP2 (for testing purposes only)

Bare metal

Management tools

Virtual Center

VMotion migration tool

System Center VM Manager (beta)

Administrator Console

Support resources

High

Medium

Medium

Advantages

  • Widest selection of pre-built appliances
  • Widest selection of guest OS support
  • Wizards galore for install aids
  • Can run on any IE browser with Internet access
  • Less expensive option
  • Easy cloning of VM images

Open source solution that doesn't require any host OS

Disadvantages

Confusing array of pricing and configuration options

Only four "virtual hard disk" pre-built appliances of MS server products

  • Limited hardware support
  • Limited Windows guest OS support
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