That idea may sound crazy, but the burgeoning trend of server virtualization makes it a reality. Using virtualization software, one physical server can be partitioned into many "virtual machines," each of which runs its own server OS and can network transparently with your existing servers. Each physical server can theoretically be split into several, dozens--or even hundreds--of virtual servers, performing whatever server function you need, such as file, print, or Web serving.
While virtual servers have been around quite a while--think IBM mainframes running VM/370--it's only in the last few years that mainframe-class virtual servers have invaded Intel territory. Driven by rising interest in server consolidation, companies such as VMware, Connectix, and SWsoft now offer server virtualization products.
Building on its success with VMware Workstation, which lets you run multiple virtual machines for desktop OSs (useful for development environments), VMware, has expanded its virtual machine technology to the server arena with its GSX Server and ESX Server products. Both let you run multiple server OSs concurrently, but each takes a different approach. GSX Server lets you run virtual server sessions (in virtual machines, or VMs) as applications on top of a host OS, providing a way to consolidate or expand the data center with a minimum of disturbance to your existing server fleet. Of course, such ease comes at a price--in this case, the cost of the system resources required to run multiple VMs on top of an existing host OS (e.g., running virtual Windows 2000 Server session on a Windows 2000 Server host). GSX Server's successor, ESX Server, obviates these performance limitations by providing its own ground-up platform for running virtual servers, using separate partitions to isolate each VM. Such an approach ups the ante in terms of mainframe-like performance, providing a pool of computing resources that can be allocated dynamically to any virtual server based on current needs.
Connectix--best known for Virtual PC, a desktop-class product like VMware Workstation--recently threw its hat into the virtual server ring with the aptly named "Virtual Server." On the surface, Virtual Server seems analogous to VMware's GSX Server, in that it can run concurrent virtual server sessions on top of an existing host OS. Connectix, however, insists the product should be compared to the higher-end ESX Server in terms of functionality and performance; but since the product has yet to ship, the verdict on this is still out.
A third entrant in the virtual server race is SWsoft, whose Virtuozzo product takes a slightly different tack with server virtualization. Virtuozzo uses an approach that SWsoft calls "virtual environments" (VEs) rather than VMs. According to SWsoft, VEs are differentiated from VMs by the ability to virtualize the base kernel of an OS for resource allocation among partitions, ostensibly providing greater efficiency and easier management. Aimed primarily at large data centers, hosting service providers, and SMBs, Virtuozzo boasts scalability to the tune of thousands of concurrent VEs on a single physical system. But like Virtual Server, Virtuozzo is limited in terms of OS support, currently supporting only Linux and FreeBSD host OS environments.
As a proven way to lower TCO and increase ROI, server virtualization is a trend that can't be ignored. And as more companies jump into the fray, the capabilities of virtual server environments are bound to increase by leaps and bounds. Enterprises looking for a way to cut costs with server consolidation servers would be well advised to investigate virtual server technology as a solution.