Although most server virtualization products work at the single-server level,
Virtual Iron Software's Virtual Iron represents a new class of server-oriented
virtualization products. Based on Xen 3.0, Virtual Iron clusters multiple physical
servers to create a scalable virtual system that you can partition into multiple
virtual servers.
Application Virtualization
Application virtualization is a new variation of virtualization technology that
solves the problems of conflicts and incompatibility between applications. For
example, application virtualization software lets you run multiple versions
of Microsoft Office on the same system or install beta software without worrying
about corrupting your desktop.
Unlike virtualization products that let you run VMs, application virtualization
doesn't provide system hardware or OS-level virtualization. Instead, it abstracts
the file system and the registry for the virtualized applications. An application
virtualization product lets you run virtual applications as if they were regular
applications, but the virtual applications leave no footprint in the system
registry or file system. Some benefits of application virtualization products
are that you can install and run applications without worrying that one application
might conflict with another or that an application will corrupt the registry,
and you can freely install and test beta software without fear that it will
corrupt the base system. And yes, you can combine virtual applications with
virtual desktop and server products, run virtual applications on VMs, and install
application virtualization products on VMs. Figure
2 illustrates the concept behind application virtualization software.
There are two main players in the application virtualization space: Softricity
(recently purchased by Microsoft) with its SoftGrid Desktop product, and Altiris
and its Software Virtualization Solution (SVS). The first application virtualization
product on the market, SoftGrid Desktop virtualizes all aspects of the client
and provides streaming application deployment. Unlike SVS, SoftGrid requires
an Active Directory (AD) infrastructure, prepackaging the virtualized application,
and a physical server system for streaming deployment.
SVS is a newcomer to the virtual application arena. SVS doesn't virtualize
all aspects of the client. Certain functions, such as system and COM calls,
aren't virtualized; only calls to the file system and registry are virtualized.
However, SVS virtualizes important objects, such as the registry and file system,
and has minimal infrastructure and virtual application setup requirements.
Hardware-Enabled Virtualization
In combination with processor enhancements by Intel and AMD, Microsoft technology
enhancements are driving the future of server virtualization.
Virtualization software provides tremendous flexibility, but the overhead of
maintaining the VM environment adversely affects the performance of virtualization
software. Although there are exceptions, VMs typically don't perform as well
as hardware-based systems do. Moving part of the support for virtualization
into the hardware reduces system overhead and results in better VM performance.
However, hardware virtualization requires support from the hardware as well
as from the host OS.
On the hardware side, Intel and AMD added logic to their processors to support
virtualization. Intel Virtualization Technology is part of the new Dual-Core
Intel Xeon and Dual-Core Intel Itanium 2 processor lines. AMD Virtualization
Technology is included in the upcoming AMD Opteron line of processors. On the
software side, Longhorn Server will support hardware virtualization through
Microsoft's new hypervisor technology, as Figure
3 shows. The hypervisor enables the OS to take advantage of the new hardware
virtualization support provided by the latest generation of Intel and AMD processors.
The end result should be better VM performance and a lower cost. The VM images
that Virtual Server 2005 and Virtual PC use will be compatible with future hypervisor
VM support.
A Virtual Reality
Virtualization technologies are a reality today. Desktop and server virtualization
is an established and mature technology that provides benefits for a number
of common scenarios, including development, testing, server consolidation, and
disaster recovery. Application virtualization is a newer technology that addresses
the problems of application conflict and system stability. Today's virtualization
solutions are software-based, but future hardware-enabled virtualization scenarios
promise to reduce the overhead of virtualization environments and significantly
improve VM performance.