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VMware or Microsoft? The virtual server choice is yours

IT managers looking for greater server efficiency and flexibility can choose from two major providers of virtual machine software: VMware and Microsoft. Illuminata analyst Thomas J. Deane compares those vendors' product options and how they stack up.

This is part of an ongoing series of articles on virtualization technology in the Windows enterprise. In future installments, we'll look at virtualization and workload management tools as alternatives or complements to VMs.

A few years go, before Microsoft acquired virtual machine (VM) technology from Connectix Corp. in early 2003, VMware Inc. was the only game in town for VM environments. Today, Windows IT managers looking for greater server efficiency and flexibility can choose from among the products of the two major players: VMware and Microsoft.

What are the product options and -- more importantly -- how do they stack up? Let's take a look.

VMware's GSX Server and ESX Server compete with Microsoft's Virtual Server 2005. All three products run multiple workloads on

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 a single x86 server, almost as though they were running on separate systems. Consolidation of server workloads into fewer physical machines = lower hardware and administration costs = Ka-ching!

VMware comes in two server flavors. Virtual machines on GSX Server run on a host operating system, which can be either Windows or Linux. An administrator first installs the host OS, then GSX Server as an application. Multiple VMs can then be created within -- or rather on top of -- GSX. The administrator then installs a guest OS and applications in each VM, as if they were installing on a new piece of hardware.

In contrast, VMware's ESX Server installs directly on "the bare metal." ESX-based VMs are created and managed just as in GSX. But because ESX Server uses a smaller, optimized microkernel or hypervisor in place of the host OS, it's substantially more efficient. ESX supports fewer hardware options than Windows or Linux, but its greater efficiency is just one reason ESX Server is the premiere VM for enterprise applications on x86 equipment.

Microsoft: New kid on the block

Virtual Server 2005, broadly a part of Microsoft's autonomic computing plan (a.k.a. Dynamic Systems Initiative), at the product level is akin to VMware's GSX. It similarly requires a host OS -- Windows Server 2003 -- and it similarly trades away performance for ease of installation and broad hardware support. Virtual Server 2005 is a young product; some of its sharp corners have yet to be rounded off. Creating VMs and associated virtual hard disk and network resources, for example, is a little bit more manual than with VMware. But the difference in costs and what it supports is what administrators will notice most about Virtual Server.

Microsoft is the newcomer and, as such, is pricing aggressively -- about one-third the cost of VMware GSX. At first glance, that's quite impressive. Unfortunately, it relates only to Virtual Server software itself. Total system costs will be dominated by charges for the server, storage, host and guest OSs, middleware and applications. Even when consolidating five workloads onto one server, Microsoft still charges as though there were five servers -- or really, six, counting the host OS. Any savings must come from hardware and admin charges; no vendor, including Microsoft, wants to reduce its own take!

For those running Windows-only or Windows-mostly shops, Virtual Server is a serious option. In its favor, it will keep VMware sharp on pricing. On the other hand, Virtual Server 2005 is limited by being an entirely Windows-focused solution in a multi-vendor world. Virtual Server 2005 runs only on Windows (only the latest versions at that), and it supports only Windows as guest operating systems (but adding Windows 2000 and Windows NT 4.0).

Versatile VMware

VMware is more expensive than Microsoft's version, especially at a component level. But it's also longer-proven and far more heterogeneous than young Virtual Server. GSX Server runs atop Windows or Linux (multiple versions, including Windows 2000) and supports many guest operating systems, including Windows versions back to 3.1, NetWare, multiple Linux distros, even BSD Unix and Solaris x86.

VMware also extends further. One can, for instance, upgrade to its optimized ESX Server for more demanding production workloads. It also offers sophisticated management tools. VirtualCenter, for instance, provides a central control point for starting, stopping and managing VMs across multiple machines. This facilitates server farm load-balancing by moving VMs from machine to machine. VMs hosted by GSX Server still must be stopped, moved and then restarted.

VMware's optional VMotion product goes one step further, allowing admins to move active VMs from system to system, on the fly, with essentially zero downtime. VMotion only works with ESX Server and a sophisticated infrastructure, including a Fibre Channel SAN shared among physical servers. But it shows the extra steps VMware has taken.

All three products reduce costs by recapturing the unused power of under-utilized servers and simplifying workload management. In about a year, advanced processors from Intel Corp. and Advanced Micro Devices Inc. will provide even richer virtualization options.

The trick is -- and will be -- deciding which solution works best and at what price.

Thomas J. Deane is a research analyst at Illuminata. He has worked in the computer industry for more that 25 years and is a Microsoft Certified Systems Engineer (MCSE) and Microsoft Certified Systems Administrator (MCSA). He can be reached at

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