One of the most important assets that a system manager brings
to any performance evaluation is an understanding of the normal
work load and behavior of the system. Each system manager must assume
the responsibility for understanding the system's work load sufficiently
to be able to recognize normal and abnormal behavior; to predict
the effects of changes in applications, operations, or usage; and
to recognize typical throughput rates. The system manager should
be able to answer such questions as the following ones:
What is the typical number of users
on the system at any given time of day?
What is the typical response time for various tasks
for this number of users, at any given hour of operation?
What are the peak hours of operation?
Which jobs typically run at which time of day?
Which commonly run jobs are intensive consumers
of the CPU, memory, and disk space?
Which applications involve the most image activations?
Which parts of the system software, if any, have
been modified or user-written, such as device drivers?
Do any known, or anticipated, system bottlenecks
exist?
If you are new to the OpenVMS operating system or to system
management, you should observe system operation using the following
tools:
Monitor utility
Accounting utility
SHOW commands (available through DCL)
OpenVMS Performance Management provides detailed procedures for using the Monitor
utility and, to a lesser extent, other operating system tools to
observe and evaluate system performance. Also, the HP OpenVMS System Management Utilities Reference Manual provides
reference information about using the Monitor utility.
Over time you will learn about metrics such as the typical
page fault rate for your system, the typical CPU usage, the normal
memory usage, and typical modes of operation. You will begin to
see how certain activities affect system performance and how the
number of users or the time of day affects some of the values.
As you continue to monitor your system, you will come to know
what range of values is acceptable, and you will be better prepared
to use these same tools, together with your knowledge, to detect
unusual conditions. Routine evaluation of the system is critical
for effective performance management. The best way to avoid problems
is to anticipate them; you should not wait for problems to develop
before you learn how the system performs.
You can learn more about your system's operation if
you use the Monitor and Accounting utilities on a regular basis
to capture and analyze certain key data items. By observing and collecting
this data, you will also be able to see usage trends and predict
when your system may reach its capacity.
You should also understand that system resources are used
by system management tools. Be careful, therefore, in selecting
the items you want to measure and the frequency with which you collect
the data. If you use the tools excessively, the consumption of system
resources to collect, store, and analyze the data can distort your
picture of the system's work load and capacity. The best approach
is to have a plan for collecting and analyzing the data.