Page 121 -

The Greening of IT
86 How Companies Can Make a Difference for the Environment

There are many aspects to IT virtualization. This chapter structure covers
the rational, server virtualization, storage virtualization, client virtualization,
grid and cloud concepts, cluster architecture for virtual systems, and
conclusions.
Over the past 30 or more years, data centers have gone from housing
exclusively large mainframe computers to housing hundreds of smaller
®
servers running versions of the Windows operating system or Unix or
®
Linux operating systems. Often the smaller servers were originally distrib-
uted throughout the company, with small Windows servers available for each
department in a company. During the past few years, for reasons of support,
security, and more-efficient operations, most of these distributed servers have
moved back to the central data center. The advent of ubiquitous high-speed
networks has eliminated the need for a server in the same building. These
days, network access even to our homes through high-speed networks such as
DSL and cable allows network performance from our homes or distributed
offices to the central data center to be about equivalent to performance when
your office is in the same building as the data center. The Internet was and
remains the most-significant driving force behind the availability of high-
ptg
speed networks everywhere in the world—including to homes in most of the
developed world. When we access a Web site from our home, from the air-
port with a wireless connection, or from the countryside using a PDA or an
air card with our laptop, we have a high-speed connection to a server in some
data center. If the Web site is a popular site such as Google, the connection
might be routed to any one of many large data centers.
When the distributed servers that had been in office buildings were
moved in the past ten years to centralized data centers, operations and main-
tenance became greatly simplified. With a company server at a centralized
data center, you could now call the help desk on Sunday morning and find
out why you had no access, and central operations could have a technician
“reboot” the server if it had gone down. So, the centralized data center pro-
vides many advantages—especially with high-speed networks that eliminate
network performance concerns. However, with the rapid growth in servers
used in business, entertainment, and communications, the typical data center
grew from dozens of separate physical servers to hundreds of servers, and
sometimes to thousands. Purchasing, operating, and maintaining hundreds
of separate physical servers became expensive. The innovative solution was to
consolidate perhaps ten of the separate servers into one bigger physical server,
but make it appear as if there were still ten separate servers. Each of the ten