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6: A Most-Significant Step—“Virtualizing” Your IT Systems 87

virtual servers could retain its own server name, its own Internet address (IP
address) and appear—even to web developers—to be a separate physical
machine (as it had been before becoming a virtual server). Costs go way down
because one large physical box is much less expensive to buy than ten smaller
physical boxes. Also, it’s significantly less expensive to maintain and operate
(“take care of”) one big server than ten smaller servers. The analogy might be
exaggerated—but it’s a bit like taking care of one big house rather than ten
separate smaller houses.
In simple terms, server virtualization offers a way to help consolidate a
large number of individual small machines on one larger server, easing man-
ageability and more efficiently using system resources by allowing them to
be prioritized and allocated to the workloads needing them most at any given
point in time. Thus, you can reduce the need to over-provision for individual
workload spikes.
In general, virtualization at the data center is applied broadly—not just to
server virtualization. It provides the capability to simulate the availability of
hardware that might not be present in a sufficient amount—or at all!
Virtualization uses the available physical resources as a shared pool to emu-
ptg
late missing physical resources. Virtualization is capable of fine control over
how and to what extent a physical resource is used by a specific virtual
machine or server. Thus, we have the concept of virtual computer memory
(which is not real memory but appears to be real) and virtual data storage.
This chapter gives details on virtualization technologies at the data center
and explains how those technologies are usually the first and most-important
step we can take in creating energy-efficient and green data centers.

The Concepts of Consolidation and Virtualization

In Chapter 2, “The Basics of Green IT,” Figure 2.2, shows an overall strat-
egy for moving to a green data center. The IT infrastructure energy-efficiency
strategy consists of centralizing data centers, consolidating IT resources at
those data centers, virtualizing the physical IT resources, and integrating
applications. Server consolidation and server virtualization both reduce
energy use by reducing the number of physical servers, but they use different
methods. Server virtualization enables you to keep all your servers, but they
become virtual servers when many physical servers share the same physical
machine. The diagrams and descriptions of the concepts of consolidation and
virtualization were based on the descriptions in the IBM red paper, “The