Introduction to Virtualization - Oracle Solaris 10 System Virtualization Essentials - page 20

the one test environment running. Many teams can share one system, achieving a
small number of test systems with little unscheduled time.
Performance testing in virtualized environments is appropriate only if the
workload will be deployed in a VE. Similar resource controls should be applied to
the test and production environments.
Another advantage of testing with VEs is the ability to take a snapshot (a point-
in-time image) of a VE and save it to disk. This snapshot can be copied, and the
copy may then be used to ensure that each successive iteration starts from exactly
the same state, with the same system configuration and test data.
1.1.6.5 Simplifying Workload Mobility
Systems should originally be configured with sufficient excess resource capacity
to accommodate expected growth in workload needs. Workloads occasionally out-
grow the physical capacity of the system. If the computer was purchased with
empty slots (e.g., for CPU or memory), additional resources can be added to the
system to expand it and accommodate this growth.
Figure 1.9 shows a system at three points in time. In the first instance, the
system is partially filled with a type of component, such as CPUs; the workload
uses only a portion of the available resource. In the middle snapshot, the workload
has grown to the point where it is consuming almost all of the physical resource.
However, the system was purchased without a full complement of that resource.
After filling the available physical slots, as shown in the last snapshot, the work-
load can grow even further without suffering performance problems.
Figure 1.9 Accommodating a Growing Workload with Additional Resources
At some point, however, further system enhancements are neither possible nor
desirable. Although in some cases the workload can be broken down into multiple
components and run on multiple small systems, this solution is rarely appropriate.
Instead, the workload must be moved to a new, larger system. Without virtualiza-
tion, that process can be time-consuming and involve many manual, error-prone