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Chapter 1: Overview of Virtualization
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Running multiple virtual servers on a single physical hardware system is generally known as “ server
consolidation. ” Historically, this meant hosting multiple server processes and their associated services
on a single, physical system, increasing the importance of that system but heightening its potential to be
a single point of failure for multiple services. Today, server consolidation means running multiple virtual
machines on a single physical system. As you ’ ll see throughout this book, server virtualization software
such as Xen can help eliminate single points of failure in your IT infrastructure by providing portable
virtual servers that can easily be moved from one physical host to another in the event of emerging
problems, or which can quickly be restarted on other physical systems in the event of sudden,
catastrophic failures.
Reduction in New Hardware Costs
The flip side of getting more mileage out of your existing servers is that, in many cases, you will not
have to buy new physical hardware in order to deploy additional servers or services. As your business
grows, deploying additional servers to better support the online capabilities that your users and
customers require is a cost of being successful. Additional Web servers, new file servers for different
groups or to handle increased load, new content management or intranet systems, and other similar
systems are frequently added to enterprise environments as both the loads on existing systems and the
number of users in general expands.
Combining server consolidation with capacity planning can reduce the number of new machines that
you have to buy to support new and existing services by making better use of existing systems. In some
cases, server consolidation may not eliminate the cost of new hardware, but it can simply reduce that
cost. For example, buying additional memory or additional network interface cards for existing systems
can enable you to expand their capabilities so that they can support additional virtual machines, without
having to buy complete, new systems.
Reduction in IT Infrastructure Costs
The previous sections discussed how server consolidation can help you make the most of your existing
hardware investments and reduce new hardware costs by enabling you to run multiple virtual servers
on single hardware platforms. However, saving the cost of purchasing and deploying new servers isn ’ t
the only IT cost reduction associated with virtualization.
Machine rooms have a variety of per - machine infrastructure costs that you can reduce (or at least avoid
increasing) by getting more mileage out of your existing hardware rather than adding new systems. Each
new physical server uses a certain amount of power and places additional load on your cooling system.
Virtual machines added to existing computer systems do not add to either of these loads, enabling you
to add more servers with no increase in power and cooling requirements. Similarly, if you are able to
consolidate multiple existing servers onto a lesser number of server systems, you can actually reduce
your immediate power and cooling costs.
During server consolidation, you can often combine hardware from physical servers to increase the
capacity of the remaining machines. For example, you can add the memory from a decommissioned
system to another server that now supports multiple virtual machines. Similarly, hard drives that
formerly provided local storage in decommissioned machines can be reused as spares, for backups, in
RAID systems, and so on.
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