In-Depth

Contenders in Virtualization

You've given your servers and desktops a thorough look prior to virtualizing them. It's time to check out a few of the solutions -- separating hype from fact.

• By Greg Shields
• 06/28/2007

In this part, we're still not yet to the installation point. Let's step back a little and look at some of the more popular virtualization software that exists on the market. Though much of the hype surrounding virtualization tries to drive businesses into a few expensive options, companies looking for low-cost virtualization can turn to a number of viable solutions.

All of the ones I discuss here make excellent contenders, depending on the needs of your business and the types of servers you want to virtualize. Let's look at the four options:

Surprising VMware Solutions
Among the four, two come from VMware. The first, VMware's most expensive solution, VMware Virtual Infrastructure, is great for enterprise-level data centers with high uptime requirements.

What you get with VMware's Virtual Infrastructure product at its Enterprise Edition level is the ability to connect your virtual server host machines to a storage area network (SAN). This enables the ability to "hot migrate" or "VMotion" your virtual machines from one physical host to another while they're still running. Some additional features, like dynamic load balancing across physical hosts and the ability to automatically reboot virtual machines on another host when a host fails, are available as well. But all these extra technologies rely on VMware's cornerstone VMotion capability.

Where a lot of people in smaller organizations get caught up in the hype is in focusing on the hipness of VMotion. That's not to say that it isn't cool, which it is. But it's also very expensive, both in licensing costs as well as the needed infrastructure (SAN storage et al.) to make it work. Many organizations don't have a very high uptime requirement for their servers. So for many, this added feature may not be worth the added cost.

VMware also quietly supports lower-level versions of its top-tier product. These versions do not have the same SAN-based capabilities and don't support the VMotion feature. With Virtual Infrastructure Starter Edition, you can host your servers on local, direct-attached storage only. Standard Edition goes a step further by enabling SAN storage support, but without VMotion. Both editions are substantially less expensive than the enterprise product.

Remember that for any version of the product -- indeed, with any virtualization product -- the ability to do a "cold migration" is always possible. The idea of a cold migration is a copy from one virtual server host to another of the virtual machine's files while it is powered off. This process does incur an outage. But if your organization's uptime needs can support it, you can break into virtualization at a much lower cost.

The other option is VMware's no-cost VMware Server product that offers much of the same capabilities, but with some obvious omissions. VMware Server is an excellent option for organizations whose servers need not be of high performance (see the first part of this series for an explanation on server performance needs for virtualization) and can stand the occasional outage. Though virtual server performance with VMware Server is lower than with the enterprise product, it's a viable substitute for smaller businesses or lower uptime requirements.

What causes many organizations to immediately discount VMware Server is that they don't realize paid support options and centralized management options are available. Though these add-ons involve added cost, that cost is minimal. VMware VirtualCenter for VMware Server is a management tool that allows for the centralized management of all VMware Server instances in the network and greatly enhances the efficiency of the VMware Server administrator. Paid support options mean that VMware Server instances that incur problems can be called in for assistance.

Some of the performance lag experienced by VMware Server can be overcome by moving the underlying operating system from Microsoft Windows Server to Linux. Much of VMware Server's performance issues relate to its installation "on top" of another operating system, rather than being an OS all to itself. For a savvy Linux administrator, installing VMware Server onto a heavily trimmed-down Linux host can regain some of that lost performance.

Microsoft Gains Virtual Ground
Microsoft's Virtual Server 2005 is also gaining some fans, and is an excellent option for those environments that either have special licensing agreements with Microsoft or are interested in maintaining Microsoft homogeneity within the environment.

Microsoft Virtual Server 2005 R2 is an often overlooked option to VMware's products, and has the tendency to actually run some OSes faster than VMware, like Vista and Longhorn. As a Microsoft product, its interface will be very comfortable for administrators used to Microsoft's way of building products. And Microsoft's knowledgebase support for the product is fairly detailed. Virtual Server supports clustering, iSCSI connections to remote SAN storage and a commitment to the VHD format common to other Microsoft applications.

It also supports a lower cost than many other options. Where Microsoft currently lags in relation to the competition is in high-end support for enterprise needs like dynamic load balancing, "hot migrations" and automatic restart of virtual machines after a host failure.

The space to watch with Microsoft is an added support for virtualization expected to come shortly after the release of Longhorn. Microsoft has announced some major changes to its built-in hypervisor -- the part of the OS that handles scheduling resources among virtual machines. These changes have the possibility to substantially improve performance using Microsoft's virtualization products.

A Different Kind of Virtualization
One product that gets less press than any of our other solutions is SWSoft's Virtuozzo. A different take on the concept of virtualization, Virtuozzo doesn't monitor and maintain fully isolated and independent virtual machines like the other products. Instead, it uses a variant of snapshotting technology to partition a Windows or Linux server into as many as hundreds of separated virtual instances that are quasi-independent.

Each separate instance believes itself to be an independent server with its own uniqueness, installed applications and IP Address. But each independent server actually shares the files on the disk with each other -- sort of like a "single instance store" for virtual machines. This has the tendency to greatly improve the number of concurrently hostable virtual machines on a single server while also improving performance. An interesting bonus is that since the common files between virtual servers are shared, once you patch the common files, you've immediately patched all the virtual servers.

Virtuozzo either has or will soon release some of the same features included with VMware's Enterprise Edition solution, like "hot migrations" and dynamic load balancing. The addition of these high-end features immediately moves this product onto the leader board where VMware Virtual Infrastructure currently sits alone.

All this improvement in speed and compression percentage is great, but comes with a downside. Because all servers are linked to each other through their common files, all servers on one host must be of the same operating system type. You can't install a Linux sever onto a Windows host, because they wouldn't share files or even file systems. So SWSoft's solution really only works if your environment centralizes on a single O/S. That being said, most businesses are in this category.

Do Your Homework
So, the moral of the story is to be very careful with the hype. There are lots of ways to safely and effectively introduce virtualization into your server room with costs all over the board. The best solution for your network might not be the one that first comes to mind.

In the third and last part of this series, we'll move past the planning stages and talk about your virtualization rollout. We'll also discuss some of the native and add-on components you may want to consider for your environment for things like backups and disaster recovery.