Datasheet

Chapter 1: Overview of Virtualization
10
System - level virtualization provides some significant advantages over server or machine virtualization.
The key to all of these is that, because they share a single instance of an operating system kernel, system -
level virtualization solutions are significantly lighter weight than the complete machines (including a
kernel) required by server virtualization technologies. This enables a single physical host to support
many more “ virtual servers ” than the number of complete virtual machines that it could support.
System - level virtualization solutions such as FreeBSD ’ s chroot jails, Linux - VServer, and FreeVPS have
been used for years by businesses such as Internet Service Providers (ISPs) to provide each user with
their own virtual server, in which they can have relatively complete control (and, in some cases,
administrative privileges) without any chance of compromising the system ’ s primary security
configuration, system configuration files, and filesystem. System - level virtualization is therefore most
commonly used for server consolidation. The primary disadvantage of system - level virtualization is that
a kernel or driver problem can take down all of the system - level virtual servers supported on that system.
Why Virtualization Today?
Host Operating System
Hardware
Single Kernel
Virtual Server Virtual Server Virtual Server
Figure 1-1
This section (and the rest of this book) focuses on server and machine virtualization,
where a single host system supports multiple, independent instances of virtual
machines running various operating systems. Unless otherwise identified,
subsequent references to virtualization refer to machine virtualization.
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