Virtualization Management - Oracle Solaris 10 System Virtualization Essentials - page 307

combined with greater workload mobility will lead to a more flexible compute
environment. Let's take a look at the problems and solutions in more detail.
9.2.1 Problems
Data centers have suffered with limitations of computer technology for decades.
This section discusses some of those limitations and the problems they cause.
9.2.1.1 Limitations of Physical Computers
Physical computers have several limitations, all tied to the fact that they are phys-
ical objects containing components with fixed capabilities. The physical frame has
a volume into which a limited quantity of components can be installed. A mother-
board or system board is assigned a maximum data rate and minimum latency for
transfers between CPU and memory. It also has a maximum quantity of I/O slots
for communication with the outside world.
Physical computers do not grow or shrink easily. Ultimately, the ability to
change is related to the original cost of the computer: The least expensive comput-
ers cannot change at all. Today's netbooks have a single CPU, which is soldered
to the motherboard, and I/O is limited to one network port. In contrast, more
expensive computers have multiple CPU and/or memory sockets, some of which
can be left empty when the system is originally purchased. Even larger systems
have multiple motherboards, usually called system boards or CPU boards, that
hold CPUs and memory.
Adding a CPU, memory, or I/O controller requires an outage on most systems.
Users don't like service outages, so proper planning is strongly recommended if
systems administrators decide to take this course.
Even though larger systems can be expanded, at some point every physical com-
puter reaches its maximum performance with a particular workload. Maximum
overall system performance is usually limited by one subsystem: compute capac-
ity, memory transfer rate, or storage or network bandwidth. At a certain point,
that computer's workload or set of workloads cannot perform better, and it cannot
handle additional work. Also, new workloads cannot be added to that system,
whether they are in VEs or not.
9.2.1.2 Dynamic Resource Consumption
The resource needs of most workloads are dynamic, growing and/or shrinking
over time. Some of these changes are periodic—with the period perhaps being as
short as the 9 A . M . to 5 P . M . workday or as long as the quarterly business cycle.
Other workloads change in the same direction over time. A primary workload for
a growing business will probably grow along with it. Other workloads, especially
smaller ones, may change unpredictably as unforeseen events occur.