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OS virtualization: Parallels' Virtuozzo vs. the competition

Solution providers are generally up to speed on most virtualization technologies, except one -- OS virtualization. Compare and contrast the features of Parallels' OS virtualization software, Virtuozzo, with the features of its competitors' products.

Solution provider takeaway: Solution providers can compare the features of Parallels' OS virtualization software -- Virtuozzo -- against those of its competitors' products.

With virtualization of x86-based systems already in the mainstream implementation phase, value-added resellers (VARs) are increasingly being called on to help their customers virtualize their IT infrastructures to reduce costs and increase data center responsiveness and flexibility. And while most solution providers are up to speed on the most common hypervisor-based virtualization products (VMware, Xen and, increasingly, Microsoft's Hyper-V), many are missing the boat on an entirely different method of virtualization: OS virtualization. If you're interested in OS virtualization, a good place to start is by examining the major vendors and products: Parallels and its Virtuozzo software, Sun with Solaris Containers (embedded as a feature in Solaris64) and Librato with Librato Load Manager.

There are two ways to virtualize x86 workloads. The first and by far the most common technique is using a hypervisor-based product like VMware ESX Server or Citrix's XenServer to run multiple virtual machines on a single system. Each virtual machine is self-contained, with its own operating system instance (Linux or Windows) and application stack and is managed as if it were hosted on a separate physical system. With OS virtualization, on the other hand, a single Windows or Linux instance hosts multiple applications on a single physical system. OS virtualization is sometimes confused with application virtualization, which is more of a desktop virtualization technology that is most often used to stream applications remotely.

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The virtualization mechanism in OS virtualization is responsible for making sure that each application is isolated from the others, both for availability and security purposes, and ensures that each workload gets the appropriate level of system resources. In general, OS virtualization requires less system overhead than hypervisors to manage more simultaneous workloads. It also provides close to the same level of workload isolation and security as hypervisor-based models and can be easier to manage. However, it's important to keep in mind that this isn't an "either/or" decision -- both hypervisors and OS virtualization have a place in a modern data center, and each has unique capabilities that recommend it over the other in specific situations.

Virtuozzo OS virtualization

In the x86 world, OS virtualization has been around for quite a while. Parallels (formerly SWsoft) is perhaps best known for its Apple Macintosh offering of the same name, which allows Mac users to run Windows operating environments and applications on their systems. But the company has a long history on the server side of the business as well, having introduced its Virtuozzo OS virtualization product in 2001. The product quickly caught on with application hosting shops, service providers and ISPs that used it to achieve higher system utilization rates, allocate system resources to diverse users and keep workloads secure.

Virtuozzo works with current Linux and Windows operating systems, including the new Windows Server 2008. The company has more than 100 customers in the Fortune 500, and Virtuozzo is in production use on more than 250,000 physical servers, covering close to a million separate virtualized containers. Parallels also has partnerships with all of the major server and chip vendors, as well as a solid relationship with Microsoft.

Virtuozzo's main differentiators versus hypervisors center on overhead, virtualization flexibility, administration and cost. Virtuozzo requires significantly less overhead than hypervisor solutions, generally in the range of 1% to 5% compared with 7% to 25% for most hypervisors, leaving more of the system available to run user workloads. Customers can also virtualize a wider range of applications using Virtuozzo, including transactional databases, which often suffer from performance problems when used with hypervisors. On the administration side, customers need to manage, maintain and secure just a single OS instance, while the hypervisor model requires customers to manage many OS instances. Of course, the hypervisor vendors have worked hard to automate much of this process, but it still requires more effort to manage and maintain multiple operating systems than a single instance. Finally, OS virtualization with Virtuozzo has a lower list price than the leading hypervisor for commensurately sized systems.

These factors give Parallels a good argument that OS virtualization with Virtuozzo will lead to lower overall costs than a hypervisor-based approach.

Virtuozzo competitors

Parallels isn't the only vendor offering an OS virtualization product. Sun Microsystems has an OS virtualization feature (Solaris Containers) embedded in its Solaris64 operating system. However, Solaris Containers work only with applications running under Solaris64 -- not the much more prevalent Windows and Linux operating systems. This is a significant limitation for most customers.

Another entrant into the OS virtualization field is Librato, a young company based in Santa Clara, Calif. The company's Librato Load Manager 2.0 provides OS virtualization support for Linux and Windows Server 2003/2008 operating systems. In addition to standard OS virtualization functionality, Load Manager offers customers advanced capacity planning capabilities, including the ability to project what resources a workload would consume if not limited by its allocation. This information alerts administrators to changing demand patterns and gives them a chance to act proactively to fix capacity constraints.

At this point, Parallels' Virtuozzo and companion products deliver a broader and more technically sophisticated virtualization ecosystem than Librato Load Manager. But Librato points to the capacity planning features in Load Manager and its ability to work with unaltered Linux operating systems as solid advantages. Virtuozzo uses a paravirtualization model that requires the software to make slight modifications to the Linux kernel. This may be a concern for Linux purists, but, so far at least, it hasn't seemed to negatively affect any of Parallels' current customers.

As virtualization moves from the cutting edge to standard operating procedure, users are going to discover that hypervisors, although a valuable tool, aren't the right choice for every virtualization task. Resellers and integrators who know their way around hypervisor alternatives, like OS virtualization, can use this knowledge to give their customers unique IT optimization solutions that fit their specific needs.

About the author
Dan Olds is the founder and principal analyst at Gabriel Consulting Group Inc., a Beaverton, Ore., IT analyst and consulting firm. Dan is always interested in hearing from users on topics including virtualization, servers and vendor support issues. You can email Dan at

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