Page 123 -

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

Green Data Center: Steps for the Journey.” (See the Bibliography for author
Mike Ebbers for additional information.) These diagrams and descriptions
should clarify the difference and some of the pros and cons of the two meth-
ods: consolidation and virtualization.

Consolidation: A Key in Energy Efficiency

A common server consolidation example that I’ve seen with many projects
over the past few years is the consolidation of e-mail servers. As discussed at
the beginning of this chapter, for reasons of cost reduction and server man-
agement efficiency, there are significant advantages to moving servers to a
central data center. As part of the distributed computing architecture where
smaller servers were distributed throughout the company, we had e-mail
servers that were distributed, often one for each corporate facility with often
only a couple hundred users for each server. When the e-mail servers were
centralized, dozens of smaller servers could be consolidated onto one or two
large mail servers. This was more than consolidating the physical servers onto
one large physical server; the large centralized e-mail servers only had one
copy of the e-mail application. So, server consolidation refers to both consoli- ptg
dating physical servers and consolidating the application.
Figure 6.1 illustrates this idea of consolidation and the energy efficiencies
to be gained. Let’s assume we have four systems, each running two applica-
tions (APP). Also, each machine consumes 2 kW power, 8 kW in total.
However, as is often the case for small x86 servers, they are utilized at only
10 percent. If we can consolidate these eight applications to a single, more
powerful server and run their operation at a utilization of 70 percent with a
power usage of 4 kW, this single server can operate more energy efficiently.
In addition, if we perform a simple power management technique of switch-
ing off the previous four systems, the result is a total power consumption of
4 kW and a 70 percent utilized system.
It’s important to note that a decrease in overall power consumption is not
the only factor. Hand-in-hand with the power reduction goes the same
amount of heat load reduction and another add-on for the infrastructure. This
double reduction is the reason why consolidation is an enormous lever to
moving to a green data center.
However, a particular drawback of consolidation is that none of systems 1
through 4 is allowed to be down during the time that the respective applica-
tions are moving to the consolidated system. So, during that migration time,
higher demands on resources might occur temporarily.