Web extra: Virtualization specialists

Server virtualization comes in many forms. Here’s a look at the approaches some of the industry’s main players have taken and their products’ feature highlights.Its current Windows Virtual Server 2005 software, a no-charge download, is comparable to VMware’s free VMware Server product. It enables organizations to host virtual machines and sessions on top of the server’s existing operating system. The company plans to more closely integrate virtualization technology into the Vista operating system, which includes Microsoft’s version of a bare-metal hypervisor. A hypervisor is a thin software layer that lets a physical server run one or more virtual servers. The approach behind SWsoft’s Virtuozzo product is to virtualize the operating system, creating isolated partitions on a single physical server and OS instance, either Windows or Linux. This approach is beneficial because it addresses the virtual machine sprawl that can replace server sprawl in organizations that adopt virtualization as part of their consolidation strategies, said Carla Safigan, director of enterprise product management at SWsoft. “No matter how many virtual environments you have, you still manage only a single OS across those,” she said. The company also offers its Live Migration tool, which lets customers move applications between any two physical servers without any downtime.VMware, an EMC company, offers its enterprise-class VMware Infrastructure 3 and free VMware Server. Of the two, most government organizations will choose the former. It includes VMware’s ESX Server, which has a bare-metal hypervisor that enables full virtualization mode, in which the hypervisor can run multiple operating system and application combinations without modification. An important feature is VMotion, which lets organizations move virtual servers from one physical device to another without downtime.XenSource manages the development of the open-source Xen hypervisor. The hypervisor, which is included with most major Linux distributions, relies on paravirtualization technology. In its case, the guest operating system is modified and makes hypercalls into the hypervisor’s API to execute instructions to memory management or input/output processes, for instance. “The guest OS collaboration with the hypervisor offers security and performance benefits,” said Simon Crosby, chief technology officer at XenSource. Efforts are under way to provide interoperability between Xen and Microsoft’s virtualization offerings. XenEnterprise is XenSource’s first commercially packaged and supported solution: The Linux version of the product shipped last quarter and XenSource recently announced XenEnterprise for Windows.