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Implementing Virtualization: Page 6 of 7

• Virtual SMP: Virtual Iron's Xen 3.0-based offering leads the way with the ability support VMs with up to 32-way SMP, followed by Microsoft VSR2 with eight-way and VMware ESX Server with four-way VSMP capabilities. Of course, you're limited by the number of physical processors available on the host system itself, so 32-way SMP may seem like overkill. But with quad-core processors projected for the near future, it's not so far-fetched to anticipate and prepare for the need.

• Extended 64-bit Support: Even though few applications take full advantage of the extended memory addressing of x86-64 systems, virtualization is one way of making the best use of the new generation of high-powered servers. Both Virtual Iron and Microsoft offer full support for concurrent use of 32- and 64-bit OSes and applications, but VMware is still working on improving support for similarly mixed environments.



Alternatives to Full-Server Virtualization
A number of companies have opted to use OS partitioning for virtualization. Products like SWsoft Virtuozzo from and PolyServe Database Utility are targeted at higher-performance virtualized applications, such as databases, because of the decreased overhead afforded by hosted virtualization. They offer the same management and provisioning capabilities of full-server virtualization and provide a protected clone of the host OS environment with unique DLLs, registry entries, I/O resources and memory maps for applications to use.
For very standardized environments and some highly transactional applications, OS partitioning offers an extremely efficient method of sandboxing multiple iterations of the host OS. Partitioning can offer better memory utilization and result in much smaller virtual images, but on the other hand, all spawned versions of the host OS will be identical to the original in all aspects. For many companies, part of the goal is the creation of a single, unified resource pool that allows the use of many OSes interchangeably. Still, partitioning may be a viable alternative to full-server virtualization for smaller and less-complex environments.

• Resource Pooling: Often used synonymously with clustering, but these offerings are designed to assimilate growing pools of physical systems and provide support for seamless, and even automated, migration of VMs when required. This is different from clustering in the HPC sense, where dozens of processors in multiple physical systems can be assigned to a single task. Resource pooling, instead, presents dozens of processors as an assignable pool, but applications are not allowed to span multiple physical machines. VMware and Virtual Iron offer the most mature support for resource pooling targeted at high-availability applications, but Microsoft also offers HA capabilities with the addition of Microsoft Cluster Services.

It's worth mentioning that in all cases, seamless HA/VM migration is dependent on the availability of a shared storage environment between source and target systems—not a requirement for typical virtualization applications. In a perfectly virtualized world, processing, memory, storage and networking would exist as a large, unified resource that could be doled out as needed. Unfortunately, this utility datacenter nirvana will be some time in coming.

But We Want It Now...
If you're faced with a compelling need to virtualize the servers in your datacenter today, VMware still has the strongest combination of hardware support, OS flexibility and enterprise-class management capabilities. But if you don't have to make a move immediately, don't feel the need to rush into it. The virtualization market is still in state of flux because of new chip-assist technologies, upcoming IOV devices and changes in the virtualization vendor landscape. The opportunities they will offer for alternative virtualization options will only improve your choices in the coming 12 months.

From the best information we have today, we believe AMD-V will offer a better approach than VT-x to processor virtualization, in part because of the advanced technology available in AMD's Opteron processors.