Citrix Systems and Microsoft's management tools—XenCenter and System Center Virtual Machine Manager 2008—both manage virtualized environments based on VMware's ESX Server as well as those of their own products.

"Several of our clients are looking at using Microsoft's Hyper-V or Citrix XenServer to compliment their existing VMware ESX environment," says Chris Wolf, senior analyst for The Burton Group in Salt Lake City. "The reasoning has primarily been cost, and the other platforms provide the services they need for virtualizing branch offices as well as development, test or training environments."

Citrix's XenCenter manages the companyâ¬"s XenServer, VMware's ESX Server and Microsoft's HyperV environments. Microsoft promises its Virtual Machine Manager 2008 (VMM), which is in beta test now, to also support Xen and VMware ESX Server.

"It's not just about managing VMware enough to get customers to convert to Hyper-V, we are looking at a full management experience for both sets of users," according to Ed Yuen, technical product manager at Microsoft.

"We've gone the route of having multi-vendor management," says Yuen. "We recognize that a customer isn't going to have just Microsoft Hyper-V servers or virtual servers, they are going to have VMware racks too—and if they do, VMM will manage it."

Yuen says that Microsoft made a commitment to provide Xen management. "Obviously since the acquisition of XenServer, Citrix would be at the top of that," Yuen says.

VMware is the only virtualization vendor in the top three who hasn't anted up to managing other environments.

The company's answer of course is the old refrain: "If our customers demand it, we will consider it."

"At this point, it is definitely something we want to do, when we feel there is enough market adoption of other virtualization technologies," according to Erik Wrobel, director of product management for VMware. "Right now when we talk to customers they either have not adopted mixed environments at all or have done so in small amounts."

However, managing environments other than its own may not be to VMware's advantage, Wolf says.

"VMware currently doesn't have as much to gain by supporting products with small market penetration," Wolf says. "Rushing to support these platforms could also be viewed as VMware validating their relevance, which is something VMware is in no hurry to do."

The management of heterogeneous virtualized environments has also gained some degree of success with other management software vendors.