Datasheet

Chapter 1: Overview of Virtualization
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Virtualization is not a new concept, and has been in use for decades in the different ways highlighted in
the previous section. However, virtualization is more popular now than ever because it is now an option
for a larger group of users and system administrators than ever before. There are several general reasons
for the increasing popularity of virtualization:
The power and performance of commodity x86 hardware continues to increase. Processors are
faster than ever, support more memory than ever, and the latest multi - core processors literally
enable single systems to perform multiple tasks simultaneously. These factors combine to
increase the chance that your hardware may be under utilized. As discussed later in this chapter,
virtualization provides an excellent way of getting the most out of existing hardware while
reducing many other IT costs.
The integration of direct support for hardware - level virtualization in the latest generations of
Intel and AMD processors, motherboards, and related firmware has made virtualization on
commodity hardware more powerful than ever before. See the section “ Hardware Requirements
for Xen ” in Chapter 3 for an overview of virtualization support in commodity hardware .
A wide variety of virtualization products for both desktop and server systems running on
commodity x86 hardware have emerged, are still emerging, and have become extremely
popular. Many of these (like Xen) are open source software and are attractive from both a
capability and cost perspective. The section “ Other Popular Virtualization Software ” in Chapter 2
provides an overview of well - known virtualization products (other than Xen) that support
commodity hardware.
More accessible, powerful, and flexible than ever before, virtualization is continuing to prove its worth
in business and academic environments all over the world. The next two sections explore some of the
specific reasons why virtualization can benefit your computing infrastructure and also discuss some of
the issues that you must consider before selecting virtualization as a solution to your infrastructure
requirements.
Basic Approaches to Virtual Systems
The section “ What Is Virtualization? ” highlighted the different ways in which the term “ virtualization ”
is popularly used today and discussed different approaches to virtualization in each domain. This
section provides a slightly different view of these same concepts, focusing on the type of virtualization
that is the topic of this book, where a single physical machine can host multiple virtual machines. This
section makes it easier to compare different approaches to running virtual machines on physical
hardware by focusing on the underlying technology rather than on terminology and by providing a
cheat sheet for general approaches to these types of virtual machines.
The most common approaches to virtual computer systems used today are the following:
Shared kernel: A single operating system kernel supports multiple virtual systems. Each virtual
system has its own root filesystem. Because all virtual machines share the same operating
system kernel, the libraries and utilities executed by these virtual machines must also have been
compiled for the same hardware and instruction set as the physical machine on which the
virtual systems are running. For more details on this approach to virtualization and some
examples of virtualization software that use this approach, see Figure 1 - 1 and the section earlier
in this chapter entitled “ System - Level or Operating System Virtualization. ” For details on any of
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