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

Server Virtualization

This section discusses the techniques that are available for server virtual-
ization, the most attractive approach to consolidation. In many cases, it is the
easiest and most-effective way to transfer workload from inefficient, under-
utilized systems to efficient, well-utilized equipment.

Partitioning

Partitioning is sometimes confused with virtualization, but the partition-
ing feature is really a tool that supports virtualization. Partitioning is the
capability of a computer system to connect its pool of resources (CPU, mem-
ory, and I/O) together to form a single instance of a working computer or
logical partition (LPAR). Many of these LPARs can be defined on a single
machine, if resources are available. Of course, other restrictions apply, such as
the total number of LPARs a machine can support. The power supplied to
the existing physical computer system is now used for all these logical sys-
tems, yet these logical systems operate completely independently from one
ptg
another. LPARs have been available on the IBM System z since the late 1980s
and on System p® since approximately 2000. Although the System z and
System p partitioning features differ in their technical implementations,
both provide a way to divide up a physical system into several independent
logical systems.

Other Virtualization Techniques

Many virtualization techniques are available, in addition to partitioning.
Popular in the market are the VMware products, Xen and Microsoft Virtual
Server. Also, hardware manufacturers extend their products to support virtu-
alization.
VMware ESX Server and Microsoft Virtual Server come with a hypervisor
that is transparent to the virtual machine’s operating system. These products
fall into the full virtualization category. Their advantage is their transparency
to the virtualized system. An application stack bound to a certain operating
system can easily be virtualized, if the operating system is supported by the
product.
VMware offers a technology for moving servers called VMotion. By com-
pletely virtualizing servers, storage, and networking, an entire running virtual
machine can be moved instantaneously from one server to another. VMware’s