Only one hypervisor currently meets every enterprise requirement and that is from VMware, said analyst house Burton Group. But it warned that its research showed that rivals Citrix, Microsoft and Virtual Iron are closing in on that goal.

Burton said that VMware, long the market share leader in x86 virtualisation, offers 100 percent of the features required to run enterprise-class, production workloads with the vSphere hypervisor.

Citrix XenServer and Virtual Iron are nipping at VMware's heels with 85 percent and 83 percent of requirements met, respectively, while Microsoft's Hyper-V lags behind with 78 percent of requirements met.

The Burton Group evaluates hypervisors based on an extensive list of criteria within the categories of high availability, live migration, memory management, networking, storage, security, compute, paravirtualisation, management, power management, and licensing and support.

The analyst firm presented its research this week to help customers figure out which hypervisors meet their needs, and which features are truly important as opposed to simply being "marketing checkboxes."

"Hypervisor vendors would all have you believe they are better than the other guy, but their product data sheets never tell the whole story," said Burton Group analyst Chris Wolf.

The Burton Group divided features into three categories: those required to operate production workloads; preferred features that are important but not required; and features that are simply optional.

For example, high availability capabilities including the elimination of single points of failure and scalability to at least eight physical nodes are required for production. Live migration, the ability to move running virtual machines (VM) from one host to another, is required. Other required features include support of hardware-assisted memory virtualisation; support for iSCSI and Fibre Channel networked storage; security features including role-based access controls and auditing of administrative actions; and hypervisor licensing based on each physical server instance.

Examples of preferred features include memory overcommit; centralised virtual switch management; an integrated firewall; centralised hypervisor patch management; and automated VM provisioning.

Examples of optional features include automated server shutdown and start-up to conserve power; integration with third-party high availability software; and integration with storage virtualisation appliances.

In addition to meeting 100 percent of required features, VMware holds the lead by offering more than 80 percent of preferred and optional features.

Citrix, at 85 percent of required features, falls short mainly in the security realm. Security logging and auditing of administrative actions; directory services integration; and role-based access controls are all missing from XenServer 5.0. However, directory services and role-based access control are expected to be added in the 5.5 version, Wolf said. Citrix is close to being ready for enterprise workloads, Wolf said.

Citrix offers 50 percent of preferred features and 58 percent of optional ones.

Virtual Iron, which is being purchased by Oracle, checks in at 83 percent of required features. Missing elements include an enterprise-class support policy; hot-add (the ability to add storage to a virtual server while it's running); a fault-tolerant management server; and integration with third-party management tools. Virtual Iron provides 46 percent of preferred features and 36 percent of optional elements.

Microsoft's Hyper-V offers 78 percent of required features but is missing live migration; hot-add; fault-tolerant management; hardware-assisted memory virtualisation; and ability to provide a minimum of two virtual CPUs for each guest operating system. Microsoft also does not meet every high availability requirement detailed by the Burton Group. Microsoft has promised to add live migration to its hypervisor, but has not yet made the feature available.

Microsoft offers 43 percent of preferred features and 68 percent of optional ones.

These four hypervisors aren't the only ones on the market; Burton Group only recently devised its criteria and is evaluating them in order of market share and requests from clients. Wolf said other vendors to be evaluated in the future include Novell, Red Hat, Oracle and Parallels.

Although the guidelines seem pretty clear-cut, Wolf said each IT shop has to evaluate its own needs and choose a hypervisor accordingly. "Nothing is set in stone. You know your requirements better than anyone," Wolf's presentation stated. "Define your organisation's virtualisation requirements and stick to them."