Performance monitoring and capacity planning are
infamous subjects to managers of mainframe-based data centers. In
brief, an Information Technology manager must decide how much computing
resources an organization needs, when they are needed, and answer why
the "how much" estimation always changes.

Managers of distributed, client/server environments wrestle with
this problem too. But they must endure the added complexity of dealing
with multiple sites.

In supporting the functions of capacity planning and performance
monitoring, IT organizations are really assessing the service levels they provide, which are decided by customer expectations:

• What service will IT provide?
  
  The customers define this.
  
  
  
  
• What service can a given configuration provide?
  
  Provided by the IT organization, these are the goals for user performance,
  factoring in the budgetary restrictions.
  

As those associated with the mainframe data centers know, this is not
easy, and even old-hands guess wrong. The difficulties arise from
several reasons:

• Predicting the future is hard.
  
  We are dealing with future hardware and software and
  how this vaporware may work together, future users and their
  requirements, and the organization's future mission. (Pop quiz: How much
  CPU capacity did you plan for your public Web server this year? Oh,
  you didn't even plan a Web server?)
  
  
  
  
• Users can't predict the future either.
  
  Smart people always find new ways of using all of the computing
  resources available. (Pop quiz: Ask your marketing manager how
  many Web pages your organization will publish next April.)
  
  
  
  
• Distributed client/server environments are more complex
  than mainframe data centers.
  There is now a wider
  variety of potential configurations, and each new generation of
  hardware and software will introduce new capabilities and costs.
  (Pop quiz: Ask your Webmaster what Java- and VRML-enabled Web pages
  mean to your organization's network load next April.)
  
  
  
  
• The rate of change in new technologies continues to
  accelerate.
  Very often, by the time a person
  understands and feels comfortable with a new technology it is
  obsolete. Both as an institution and as individuals, IT staffs
  must keep abreast of new technologies or risk being left behind.
  (Pop quiz: Did your IT department spearhead your Web server
  development and deployment?)
  
  
  
  
• Organizations are complex.
  
  Complexity breeds specialization. Experts in one field are rarely
  experts in another. When planning computer and network use
  it helps speak the language of your constituency.
  

While some view capacity planning as an art form, you can approach it scientifically. Keep in mind it is easier to find that a
configuration will not support a specific service level than
to predict it will. For example, it is easy to determine that a
system with

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