Editor's note: Since this article was written, VMware released ESX Server 2.5. Overall, there's little difference between version 2.5 and 2.0.

It's no overstatement to say that VMware ESX Server 2.0 stands at the pinnacle of today's virtualization software technology. Unlike Microsoft Virtual Server 2005 and VMware GXS Server, ESX Server doesn't require a host OS. Instead, ESX Server runs directly on the hardware. The payoff is increased performance and improved manageability for the hosted virtual machines (VMs). However, ESX Server is supported only on systems that VMware has certified with its hardware partners.

I installed EXS Server on an HP ProLiant ML350 with dual Intel Xeon 3.2GHz processors, 2GB of RAM, and a dual-channel Ultra320 SCSI connected to four 36GB 15,000rpm hard disks. Installing ESX Server is more like installing an OS than an application. The partition you install it on is completely dedicated to ESX Server. Any data on that partition is deleted. As part of the installation process, you define a password for the root user and specify either a DHCP-assigned IP address or a manual IP address.

After the installation completes, you're left with a text-based shell. You use a Web-based interface to manage ESX Server. With this interface, you can create VMs and set various virtual hosting parameters.

ESX Server supports creating VMs for Windows, FreeBSD, Linux, and Novell NetWare. ESX Server is well adapted to server consolidation scenarios. The ESX Server host OS is lightweight. It doesn't provide GUI support or any features other than those required to run VMs. ESX Server supports very large host systems—systems with up to 64GB of RAM, 256TB of storage, and 16 processors. ESX Server can run up to 80 VMs on a single server. However, in practice, you probably wouldn't want to run that many VMs on one server.

Although ESX Server is a standalone product, customers who purchase ESX Server often buy the companion product VMware VirtualCenter. VirtualCenter extends the built-in management capabilities of both ESX Server and GSX Server. Together, ESX Server and VirtualCenter can move VMs between different ESX host servers with no downtime. (There's a delay, depending on your hardware and network capabilities, but client connections aren't lost.)

If you need to implement a data center or perform enterprise-level server consolidation, I recommend checking out ESX Server. It provides the best performance and features of any virtualization product available today. Although it costs more, it provides a level of scalability, performance, and stability that exceeds that provided by GSX Server and Virtual Server 2005. For multiple server management, VirtualCenter is a valuable addition.

Summary
VMware ESX Server 2.0

PROS: Excellent performance and manageability

CONS: Limited hardware support; advanced management features require VirtualCenter

RATING: 4.5 out of 5

PRICE: $1,875 per CPU; Virtual Infrastructure Node (a bundled package consisting of ESX Server and VirtualCenter) is available for $5,000

RECOMMENDATION: Check out if you need to implement a data center or consolidate enterprise-level servers.

CONTACT: VMware, 650-475-5000 or 877-486-9273, http://www.vmware.com