Under most conditions, tuning is rarely required for OpenVMS
systems. The AUTOGEN command procedure, which is included in the
operating system, establishes initial values for all the configuration-dependent system
parameters so that they match your particular configuration. For
information about AUTOGEN, see
Understanding the AUTOGEN Command Procedure.
Additionally, the system includes features that, in a limited
way, permit it to adjust itself dynamically during operation. That
is, the system detects the need for adjustment in certain areas,
such as the nonpaged dynamic pool, the working set size, and the
number of pages on the free and modified page lists. The system
makes rough adjustments in these areas automatically. As a result,
these areas can grow dynamically, as appropriate, during normal
operation.
Experience
has shown that a common cause of disappointment in system performance
is insufficient hardware capacity. Once the demand on a system exceeds
its capacity, adjusting system values will not result in any significant
improvements, simply because such adjustments are a means of trading
off or juggling existing resources.
Although tuning is rarely required, you should recognize that
system tuning may be needed under the following conditions:
If you have adjusted your system for
optimal performance with current resources and then acquire new capacity,
you must plan to compensate for the new configuration. In this situation,
the first and most important action is to execute the AUTOGEN command
procedure.
If you anticipate a dramatic change in your work
load, you should expect to compensate for the new work load.
HP OpenVMS System Manager's Manual, Volume 2:... 
Performance Considerations
