The virtualization marketing wars that heated up the summer competition among VMware, Microsoft and Citrix, then dampened and cooled with the winter weather, are heating up again. \nLast week, when VMware was busy hosting its VMworld Europe trade show in France, Citrix and Microsoft announced a series of new products that not only cement their alliance against VMware, but also plug many of the holes each suffers individually in comparison with VMware, according to Chris Wolf, a senior analyst for Burton Group. Red Hat used the same week to announce a whole new line of open source virtualization tools.\nOracle is throwing signs that it's ready to jump into virtualization in a more serious way as well. \nLinux-market analyst Katherine Egbert, of financial-analysis firm Jefferies & Co. published a report Monday that read, in part: "multiple industry sources seem to indicate that Oracle will soon improve its server virtualization management capabilities by purchasing privately held Virtual Iron." \nOracle's previous effort on the virtualization front was to include an open-source hypervisor customers could use under its stack of applications. Buying Virtual Iron, the fifth-largest server virtualization vendor, Egbert noted, would be a way to improve Oracle's position in the virtualization market overall. \nWhat's VMware's best response to static from competitors? Its technology is speaking for itself at the moment. Burton Group's Wolf recently authored a report that laid out the features required for a virtualization infrastructure product designed to operate as a critical part of an enterprise data center, comparing the main offerings. (See a summary of Wolf's findings in presentation format, here.)\nVMware's ESX was the only product that passed the test, Wolf says. \nIt's not the only product close to passing the test. In each of the categories there were features listed as required and others as optional. ESX met 100 percent of the requirements, but other products did fairly well, too, he says. \nNot even VMware issued an official response to the Burton Group evaluation, though Wolf says there was plenty of back-channel discussion. Microsoft Hyper-V honcho Patrick O'Rourke, a frequent contributor to Microsoft's virtualization-team blog, came closest to an on-the-record response in a comment he posted on Wolf's blog, promising that Microsoft will "prove that our collaboration with Citrix, Novell and Red Hat, as well as new features in WS08 R2 and SCVMM r2, will improve Microsoft's position in Burton's report." \n"I'm not at liberty to say who will make it next," Wolf said. "But by June another hypervisor will meet at least the required criteria." \nThe report took three months to research and put together, Wolf says. Much of the effort was in polling end-user companies for their real-world requirements for a virtual infrastructure. None of the characteristics, either required or optional, was taken from lists created by vendors. \n"For us it was the clients saying they needed this information to evaluate competing hypervisors\u2014the features that are important to them on production workloads," Wolf said. \nMicrosoft's Hyper-V, for example, failed to qualify because its live-migration capability is still in beta, and it doesn't have any native high-availability features. Microsoft relies on third parties for high-availability functions. \nIt's also missing the ability to assign priorities to particular VMs on restart, hardware-assisted memory virtualization, and fault-tolerant management capabilities. \nCitrix XenServer had no native high-availability functions until recently, Wolf says. And it has live migration built in. But it doesn't have the ability to trunk VLAN connections, integrate with directories for secure logon, or provide role-based access. \nStill, their recent announcement filled in many of their weaknesses, Wolf says. \nCitrix' main effort was in reducing the price of XenServer, its full-function hypervisor, to zero. Microsoft and VMware both offer a free hypervisor, but both are constrained in various ways. VMware's ESXi, for example, doesn't include VMotion, the ability to move a running VMware virtual server from one server to another. \nMicrosoft's Hyper-V doesn't include that feature, and won't until the next version is released this summer. But Citrix' XenServer does. It also comes with the XenCenter management console, Active Directory integration, and VM resource pooling to make it easier to create a logical unit of VMs devoted to individual user groups or geographic areas. \nCitrix also released Citrix Essentials, which includes both the free XenServer and tools to manage either Xen VMs and Windows Server 2008 Hyper-V virtual servers. The base package, which will cost about $1,500 per physical server, has dynamic provisioning and workflow to determine when and how VMs are launched, and interoperability features so applications running on XenServer VMs can be shifted to Hyper-V machines. \nLabManager and StageManager, which provide more detailed provisioning and management functions, will be part of a more expensive Essentials package. \n"That fills a lot of gaps for Citrix and Microsoft," Wolf says. "It provides some very good integration between storage provisioning and Hyper-V, which can alleviate a lot of the complexity of deploying LUNs with virtual machines. And it gives developers a shortcut to XenServer and Hyper-V." \nMost software vendors, faced with the decision of whether to develop for Microsoft or Citrix virtualization products, can develop for Citrix and, through the APIs and custom integration in the XenServer and Citrix Essentials products, link to both Citrix and Microsoft virtual infrastructures. \n"They're killing two birds with one stone," Wolf says. "They have to develop for VMware first, so deciding which to go with second is a resource-management issue. With Citrix Essentials that largely goes away." \nBy tuning its Terminal Services, Systems Management Server and Hyper-V to work well with Citrix products, Microsoft reinforces its own weaknesses in VM migration, management and storage integration, Wolf says. \n"The competition among virtualization vendors is likely to get nastier," Wolf says. "There is a perception that a lot of other companies are catching up to VMware on a feature-to-feature comparison, so they're more eager to draw comparisons." \nWhy haven't they been doing so in the past few months? They've been busy, Wolf says. \n"Almost every customer we talk to is looking at virtualization options, and most of them are looking at multiple hypervisor solutions," Wolf said. "That's keeping the vendors jumping. They're trying to keep up with the level of interest from customers."