This section discusses the techniques that are available for server virtualization, the most attractive approach to consolidation. In many cases, it is the easiest and most-effective way to transfer workload from inefficient, underutilized systems to efficient, well-utilized equipment.
Partitioning is sometimes confused with virtualization, but the partitioning feature is really a tool that supports virtualization. Partitioning is the capability of a computer system to connect its pool of resources (CPU, memory, 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 systems, yet these logical systems operate completely independently from one 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.
Virtualizing Your IT Systems is is an excerpt from
The Greening Of IT: How Companies Can Make A Difference For The Environment,
by John Lamb, published by IBM Press