Implementing Virtualization: Page 4 of 7

We decided to take a look at three full server virtualization offerings, environments capable of concurrently supporting both Windows Server 2003 and Linux on the same hardware and focused on providing and managing a unified server resource pool across multiple physical machines.

VMware
The current market leader in virtualization is VMware's enterprise product, ESX Server. This VM model employs a "service console" that is loaded on each physical machine to administer and manage the actions of the hypervisor, as well as provide support for a management agent. VMware uses a binary translation methodology to provide a common hardware platform, which means that a software layer is placed between physical and virtual devices to manage resources and to "trap and translate" OS error conditions that would normally cause the VM to crash. This approach solved the ring translation problems of legacy x86 hardware management and supported the use of any x86-compatible OS without modification, but at a price: The downside of all that flexibility is that software emulation of hardware services ultimately incurs a performance hit; how big a hit can vary dramatically. Estimates range anywhere from 10 percent to 30 percent depending on the application and to whom you're speaking. Fortunately, VMware has also benefited from chip-assist technology. The 3.0 version of ESX Server now available has undergone a number of enhancements to improve the performance of VMware's software approach and take advantage of new processor features.

Virtualization Gotchas If you're considering virtualization now, here are a few tips to help your decision process: • Know your application environment: CPU utilization is only part of the story. Factor in disk access, memory and network activity as well. A server running at 15 percent CPU utilization could well be regularly hitting the network at 60 percent or 70 percent, and even though you'll have access to many virtual NICs, a physical NIC will still have the same limitations. • Don't skimp on horsepower: An April //2006// study by the Edison Group showed that choosing top-end over entry-level processors for virtualization hosting could almost double the number of VMs a given server can support and result in a 53 to 77 percent better TCO over a three-year period. • Cover your tail: In the traditional physical datacenter there's a 1:1 relationship between systems and applications, so if a server fails, you lose only one app. If you lose a server hosting a dozen VMs it will impact a substantially larger group of users, so it pays to make sure your resource pool has sufficient failover capabilities to protect mission-critical applications. • Don't forget software licensing: When you run seven virtual instances of Server 2003 on VSR2, how many licenses will you need to own? Or, when you increase your Oracle database from four to five virtual processors, what will that do to your license agreement? The combination of multi-core processors and virtualization is making a mess of licensing, something to keep in mind as you entertain dreams of hardware cost savings. • Think big, start small: Virtualization can be easy to do on an ad-hoc basis, and many companies have chosen to start by virtualizing older servers as they age out. But don't forget that the real key to effective virtualization is management, so make sure your evaluation plan leaves enough room for growth.

ESX Server currently dominates the market for enterprise-class, multi-OS server virtualization and is backed by a mature portfolio of enterprise-class management tools offering centralized administration, live virtual server migration, automated resource scheduling, distributed file services, consolidated backups and advanced protection for high-availability environments. VMware virtual services are also designed to integrate well in datacenters already using high-end management systems, such as IBM's Tivoli and HP's OpenView.

Xen via Virtual Iron
The open-source Xen hypervisor started out as an interesting project in the University of Cambridge Computer Laboratory, and in only a few years industry buzz has grown from a ripple to a tsunami (see the history at www.cl.cam.ac.uk/Research/SRG/netos/xen/). The first versions of Xen were targeted at the Linux community and were based on a paravirtualization model that required the Linux kernel to be specifically—and painstakingly—modified to run on the Xen hypervisor. This was a one-way conversion—modified kernels could no longer run on conventional hardware without the Xen hypervisor. Paravirtualization also made it impossible to run Windows on early versions of Xen because Microsoft wasn't about to let us modify Windows.

In December 2005 the Xen development team released Xen 3.0, the first version of their freeware hypervisor that supported chip-assist technology and was finally capable of hosting any OS with the help of either VT-e or AMD-V. The impact was huge: elimination of the need for kernel modifications, thus allowing Windows to run in a Xen environment side-by-side with Linux and Solaris. But what's been missing in the Xen environment so far is the vast array of enterprise-class support tools offered by VMware Infrastructure 3 suite.

To fill this gap, members of the Cambridge Computer Labs brain trust that originated the Xen hypervisor created the company XenSource, whose virtualization management product line now includes: XenEnterprise v4, XenServer v4 and XenExpress v4. Though these products have just barely scratched the surface of the enterprise computing market, in August 2007 thin-client vendor Citrix announced plans to acquire XenSource for nearly half a billion dollars in cash and stock. This move will further cement the position of the Xen hypervisor in the virtualization landscape, and will make Citrix a player in the potentially huge server virtualization market.