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ability to copy a storage object very quickly, reducing the effects of this operation
on the service being provided.
Another advantage of VEs, even in a nonconsolidated configuration, is realized
more fully by some virtualization technologies than by others—namely, security.
Some types of VEs can be hardened to prevent users of the VE (even privileged
ones) from making changes to the system. Operating system virtualization pro-
vides the most opportunities for novel security enhancements.
Virtualization can also help prepare the organization to handle future work-
loads. If the needs of future workloads are not known, it may be easier to meet
those needs if they can be met on a per-VE basis. For example, hypervisors can
host different types of operating systems. The next workload might use software
that is available on only one operating system, which is a different OS than the
one used by the first workload.
In summary, consolidation is used to reduce the costs of acquisition and opera-
tion, and virtualization is needed to isolate one workload from another workload
so that each can operate as if it is the only workload running on the computer.
Further, virtualization can be used in some cases for the unique advantages it
brings, even on unconsolidated systems.
Many of the capabilities of VEs can be put into context and further investigated
with common use cases.
All consolidated systems require resource management features to prevent
one VE from overwhelming a finite resource and thereby preventing other VEs
from using it. This possibility is discussed in the use case “General Workload
Consolidation” (discussed later in this chapter).
All consolidated systems need firm security boundaries between VEs to prevent
one VE from interacting with another in an unintended fashion. This scenario is
discussed in the use case “Configurable Security Characteristics.”
Virtualization creates the sense—and sometimes the reality—that there is
something extra between the VE and the hardware. In some virtualization tech-
nologies, the extra layer creates performance overhead, reducing workload perfor-
mance. This overhead also reduces scalability—the ability to run many workloads
on the system. However, the separation provided by this layer can also be very
beneficial, as it provides a more well-defined boundary between workload and
hardware. This arrangement makes it easier to move a VE from one computer
to another than it is to move an OS instance from one computer to another. This
situation is discussed in the use case “Simplify Workload Mobility.”
Learning to manage virtualized environments requires modifying your think-
ing and changing some practices. Some tasks that were difficult or impossible
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