5 Ways to Make Your Capacity Plan Bullet Proof

By: Ivan Walsh

This week’s article on Capacity Planning looks at the 'Assumptions' you need flag in your plan.

Assumptions are something you need to flag in the introduction to your Capacity Plan. You can’t take anything for granted in an IT Dept, or if there are third parties involved. Flag these upfront and cover yourself.

As Al Pacino says in Insomnia, “It’s your name that goes on the report.” Hilary Swank knew what he meant and double-checked everything.

Same applies to you – it’s your career, after all.

Click here to download your Capacity Plan template

Writing a Capacity Management Plan is easier than you’d think. Most people avoid it and leave it to last. It’s also part of ITIL umbrella, which has a reputation for being obscure, difficult and heavy on paperwork. Capacity Planning is one of those documents that nobody wants to write, but once you get into it, it’s fine.

1. Why do I need to Identify Assumptions?

In the Introduction chapter of your Capacity Plan, you need to:

Identify assumptions so that the Project Stakeholders and those who will sign-off on this document fully understand the limitations, constraints or conditions that underpin the plan.

As you are responsible for the content of this document, it’s up to you to ensure that you have covered all angles so that if the Capacity Plan needs be changed, you can point out that this issue was raised in the Assumptions section.

Identify conditions relating to business scenario that may require capacity (i.e. technical resources) and how your calculations for these figures were derived.

Highlight assumptions which are beyond the control of the project but may influence its success.

Failure to identify assumption leaves you in a delicate position if the project stakeholders question that performance of your system, for example, its inability to manage heavy loads during peak periods or your dependence on a third party software.

If you're dependent on this, flag it here.

2. What are Assumptions?

Assumptions describe assumed factors (as opposed to known facts) that could undermine the information in this document and disallow you for implementing your Capacity Plan successfully.

Click here to download your Capacity Plan template

3. Examples of Assumptions?

Example of typical Assumptions include: 

• Third-party software that you rely on
• Operating environment that is outside your control
• Company policy that determines how users access, use and interact with the system
• Legislation that may change and effect your system configuration

The Capacity Plan model could be negatively affected if these assumptions are incorrect or change during the project lifecycle.

4. How to Write Assumptions?

All Assumptions have a potential Impact.

When you write your assumptions, word it so that you identify the Assumption and then describe the Impact it will have on your Capacity Plan.

Click here to download your Capacity Plan template

5. Examples of Common Assumptions

Here are some examples:

Assumption - Server utilization is limited to 75%

Impact - The server capacity sizing has been performed with the assumption that the system performs within the SLA criteria.

Assumption - Changes in Programs

Impact - This Capacity Plan does not account for performance impact of changes made to the system beyond those implemented by [enter date]. Adding new programs to existing programs will affect the application resource utilization.

Assumption - Change in Hardware Usage

Impact - This Capacity Plan assumes no changes in hardware due to modifications to program usage. Changing user programs and other application configurations will impact batch and online execution times.

Assumption - Changes in Business Processes

Impact - This plan assumes no change in performance characteristics due to changes in business process. Changes in business process may affect the execution of Batch Jobs.

Assumption - Topology Changes

Impact - This plan assumes no performance impact due to topology or architectural changes.

Assumption - Database Capacity

Impact - It is assumed that the processor utilization during batch processing will be the driving factor for database capacity.  The March 2010 batch cut-off CPU utilization data validates this assumption.

The average Daytime CPU utilization was 66% while the average Night-time CPU utilization batch cycle was 386%.

Assumption - Accuracy of Load Data for Email Services

Impact - There is insufficient information regarding load volume from email services, which share hardware with application server for online and other services.

Click here to download your Capacity Plan template

There is also insufficient data on growth of the email services load. The current capacity model does not separately account for email services for capacity estimation.

Assumption - Hardware Estimates

The baseline for creating the capacity estimate model is determined by the production resource utilization and transaction load data.

Assumption - Online transactions are processed in real time.

Impact - The peak transaction load is the limiting factor when estimating requirements for the application servers.

Assumption - Batch Processing will be process transactions in off line mode.

Impact - Batch jobs can be controlled to balance the load on servers. This means that average CPU utilization will be used for capacity planning on these servers.

These are all examples of assumptions that you may need to flag when writing your Capacity Plan.

What do you think?

If you were writing a Capacity Plan what would be the most important points, you’d cover? How else can I place the document in context so that the reader understands the scope of this exercise?

Click here to download your Capacity Plan template

What have I missed?

What mistakes do people make when scheduling batch runs and when factoring this information in the Capacity Plan?

About Ivan

Ivan Walsh helps companies like yours improve their technical documents. What’s the one question about technical writing you’d like him to answer? Ask him at www.ivanwalsh.com

PS - Click here to download this 40 page MS Word template instantly.