Tandem Capacity Model (TCM) Manual

6 Creating a Performance Model
This chapter describes how to create a Performance model (PM) for your application or set of
applications. The Performance model enables you to ask questions about system performance
under changing circumstances, such as transaction rates, response time constraints, and CPU type.
As a capacity planner, you often have a number of options regarding the system’s response to
increased workload. For example, you can add hardware to reduce CPU utilization and improve
response time. Or you can leave hardware unchanged and tolerate longer response times.
With the Performance model, you can explore possibilities by imposing constraints on the modeling
process. You can impose constraints on either hardware configuration or performance factors. For
instance, you can ask what will happen to response time if the average transaction rate doubles
but the hardware configuration remains the same. Or you can ask what is the lowest-cost
combination of CPUs and disk drives that will maintain an average response time below two
seconds.
Because the TCM Performance model bases its estimates on selected baseline data, it is important
to select a representative but conservative WA model for the Performance model to use as its input.
To select a representative model, analyze capacity history and discard samples with inconsistent
CPU and disk demands.
Creating a New Performance Model
In the following procedure, it is assumed that you have checked the WA model for the application
for reasonableness and that you have selected a representative WA model as the basis for your
analysis. For more information about checking the WA model for reasonableness, see “Checking
an Apportionment Method” (page 82).
To load the baseline data to create a new Performance model:
1. Launch TCM. The “TCM Initial Menu” (page 66) appears.
2. Select Create a New Performance Model and click OK.
The Specify Custom Directory dialog appears.
3. Specify a custom folder and click OK.
4. The Create New Performance Model dialog box appears. Select whether to load the
Performance model from a WA model or a CSV file and one of:
• A WA baseline file (when loading from a WA model)
• A CSV file and an apportionment method
When you click the WA Model button, the WA Baseline File list appears, and the Using
Apportionment field is disabled. When you click CSV File, CSV files are shown instead
of WA Baseline files, and the Using Apportionment field is active.
86 Creating a Performance Model