The server virtualisation vendor landscape

The virtual machine software market has three principal players: Microsoft, VMware and Xen. Each has its unique strengths and weaknesses, which must be assessed before a commitment to a strategic platform is made.

research A recent survey of large Australian companies found that 50 percent frequently used virtual machines to execute workloads and another 20 percent occasionally used them. In the same survey, 100 percent of organisations reported that they use SANs (storage area networks) either always or frequently.
Kevin McIsaac

The virtual machine software market has three principal players: Microsoft, VMware and Xen. Each has its unique strengths and weaknesses, which must be assessed before a commitment to a strategic platform is made.

VMware has the highest cost, dominant market share, greatest maturity and most features. It is best suited for organisations that want a low risk, fully operational solution now. Microsoft has a low cost, weaker product that may suit "Windows only" organisations with undemanding requirements. Xen is the open-source alternative with the greatest potential for 2006/2007. It best suits leading edge, high risk organisations with an open-source outlook that can wait 12 months to 18 months for a full production implementation.

VMware is the pioneer of virtual machines on x86 processors and shepherding this technology from a curiosity in 1999 to one of the fast growing software segments in 2005. They provide four versions: Workstation, Player, GSX server and ESX server. VMware provides mobility between all of these different versions, i.e. a virtual machine created in one version can (with some restrictions) be executed by another version. All VMware products support a broad range of operating systems (e.g., Windows, Linux, BSD, Solaris) within a virtual machine.

Interview with VMware co-founder Diane Green.

VMware Workstation is a desktop operating system solution aimed at developers, testers and other desktop users. It's a mature product (fifth major release), meaning it is stable and fully featured. It's a hosted virtual machine which runs as a guest of either a Windows or Linux host operating system. It can be downloaded from VMware's Web site and licensed online for US$189.

A hosted virtual machine uses the host operating system to access resources such as disk and network. While the application in the virtual machine runs natively on the CPU, the reliance on the host operating system increases overhead, reduces performance, and leaves all virtual machines vulnerable to problems with the host operating system.

VMware player is essentially a workstation without the ability to create virtual machines. It is free and can be downloaded from VMware's Web site.


VMware GSX server is designed to run departmental applications on a multi-processor server. Like Workstation, it runs as a guest of Windows or Linux, and suffers the same disadvantages. GSX Server has two pricing levels, 2-processor licence (US$1,694) or unlimited processor licence (US$3,388) where a processor may contain multiple cores. Each virtual machine is limited to a single CPU.

ESX server is the flagship solution designed for mission critical applications on a multi-processor server. It runs natively on the hardware, improving performance and reliability compared to a hosted solution. ESX server supports up to 4 CPUs per virtual machine, an increase from 2 in the previous version. Live workloads can be migrated from one machine to another without requiring down time. Migration can be between servers in the same data centre or potentially across data centres.

With a robust native implementation, virtual SMP, workload migration and advanced centralised management, VMware is the most advanced of the three products and can be used for all but the most demanding workloads (i.e., very large SMP, extreme disk or network I/O).

Microsoft has two products, Virtual PC for Windows desktop operating systems, and Virtual Server for Windows server operating systems. These products were originally developed by Connectix and were acquired by Microsoft prior to general release. Both products are hosted, with the related performance and reliability disadvantages. In April 2005 Microsoft announced it is building a native virtual machine and indicated it would appear as an update to Longhorn. Realistically we do not expect to see this before 2008, perhaps not until 2010.

Virtual Server has two licences, up to four processors (AU$862) and up to 32 processors (AU$1,741). Microsoft's products are cheaper than the VMware alternatives (i.e., Workstation and GSX); however VMware is clearly the leader in market share, maturity and functionality. Anecdotal evidence indicates that production VMware implementations vastly outnumber Microsoft, perhaps 10:1.

Without a native implementation, virtual SMP, migration of executing workloads and broad support for non Microsoft operating systems, Microsoft's product is limited compared with VMware and will only be used by Window's only organisations with undemanding workloads.

Xen is an open-source virtual machine developed by the University of Cambridge, England. It has support from many vendors, including AMD, Hewlett-Packard, Intel, IBM, Novell, Red Hat and Sun Microsystems. Xen uses a technique called paravirtualisation that unlike VMware or Microsoft's solutions may require the operating systems to be modified. The benefit is an efficient native virtual machine with far higher performance. Xen currently supports NetBSD, Linux and FreeBSD. Novell has demonstrated NetWare on Xen but Windows is not currently supported. Red Hat and Suse ship Xen as part of their package but it isn't installed by default.

Intel has contributed code to Xen to support virtualisation extensions to x86. This enables operating systems to run unmodified on hardware that supports these extensions. This means Xen will run Windows unmodified on x86 servers with virtualisation support (i.e., Intel's VT and AMD's Pacifica) with a performance boost compared with the existing solutions.

Xen can be freely downloaded from XenSource, while a centralised management solution (XenOptimizer) may be purchased from the Web site.

With version 3.0 in beta (released last December) and production versions due in the first half of 2006, Xen 3 is the product to watch. Though 2006/2007 Xen will increase pressure on VMware to lower prices and by late next year it will be the major alternative (and rival) to VMware. Xen suits leading edge organisations with an open source outlook that can wait 12 months to 18 months for a full production implementation.

Next steps
IT organisations need to develop a strategy for virtual machines. The first step is to asses the three principal players, Microsoft, VMware and Xen. Organisations requiring a low risk, fully operational solution now should favour VMware. Windows only organisations with a few undemanding requirements that need the lowest cost solution should consider Microsoft. Technical innovators looking for a leading edge solution, or those with an open source outlook, and who can wait 12 months to 18 months for a production solution should mark time and watch the evolution of Xen and revaluate it at the end of 2006.

Conclusion: 2006 will be the year that server virtualisation technology becomes mainstream on x86 based servers. IT organisations are combining commodity x86 based servers with virtual machines and SANs to build agile, low cost server infrastructure. They are reporting many benefits including excellent TCO, rapid provisioning, increased resource utilisation and simple, low cost high-availability and disaster recovery.

Of the three core technologies used to build this infrastructure, virtual machines are the newest and most rapidly evolving. In 2006, IT organisations must understand this technology, and the vendor landscape, to ensure they make the right strategic choice for the next five years.

Dr Kevin McIsaac has over 20 years of IT experience and is a recognised expert in infrastructure, operations, vendor management and the art of running IT as a business. For the last five years, Dr McIsaac worked for META Group, most recently as the Research Director Asia-Pacific, researching, distilling and disseminating best practices in IT. In that role he advised the CIOs and the IT management teams of leading Asia-Pacific organisations. Prior to joining META Group, Dr McIsaac held leadership positions at Computer Associates and Functional Software.

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