Datasheet

Chapter 1: Overview of Virtualization
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different operating systems or versions of an operating system. Server virtualization is extremely time-
and cost - effective in such situations, reducing the amount of hardware required, and also reducing or
eliminating much of the time required for system installation, re installation, and subsequent
configuration.
Server virtualization makes it easy to install software products and test against many different operating
systems or versions of operating systems without requiring dedicated hardware for each. By combining
virtual machines with storage virtualization solutions such as logical volume management, you can
eliminate the need to reinstall these test versions of an operating system in most cases by creating
snapshots of pristine operating system distributions and then falling back to the snapshot for your next
test run. Using a saved snapshot of a virtual machine is not only faster than reinstalling an entire virtual
or physical system, but it can make reinstallation unnecessary if you can roll a virtual machine back to a
pristine state via snapshots or the use of the non - persistent disks that are supported by some
virtualization solutions.
An interesting use of virtualization in system testing outside the quality assurance or system test groups
is using virtualization to test new releases of an operating system and associated software. As a specific
example, newer versions of Microsoft Windows often expose or introduce incompatibilities with existing
disk layouts, boot loaders, and so on. Testing a new operating system inside a virtual machine, as many
of my friends have done with various releases of Microsoft Vista, provides a great sandbox in which to
experiment with the new operating system, test and verify application compatibility, and so on, all
without permanently disturbing the disks, partitions, and applications on their existing systems.
Virtualization Caveats
This books primarily focuses on the advantages of virtualization. As the previous section discussed,
there are many good reasons for integrating virtualization into a computing environment. At the same
time, virtualization is not a panacea for all IT woes — it is not appropriate for all scenarios, and it
introduces real costs and concerns all its own. When considering integrating virtualization into your
computing environment, you should take issues such as the ones discussed in the next few sections into
account. Sayings like “ An ounce of prevention is worth a pound of cure ” and “ forewarned is forearmed ”
aren ’ t just fortune cookies to look for, they are as appropriate in IT management circles as they were
when planning next season ’ s crop rotations.
Single Point of Failure Problems
As discussed in the previous section, server consolidation leads to better use of your existing hardware
by enabling you to use spare processing power to run multiple virtual machines on a single host. In a
typical IT organization, each of these virtual machines runs a single server or set of related services, such
as mail servers and associated anti - SPAM software, DNS servers, print servers, file servers, and so on.
The downside of server consolidation is that it increases the potential for the failure of a single physical
machine, which hosts multiple virtual servers, to significantly impact your organization. If multiple
servers and associated services are running on individual machines, the failure of a single machine has
an impact on only a single server. When multiple servers are running as virtual machines on a single
piece of hardware, the failure of that hardware can take down all of those servers.
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