I have just added to the website a presentation that looks at sizing and extrapolation techniques for people considering building a small scale performance test environment instead of a large full scale performance test environment. In the paper several approaches are considered.
Factoring – This is where the architecture is easily scaled and therefore the performance test can be undertaken on a subset of the hardware.

Dimensioning – The architecture has known bottlenecks that drive the performance such as a central DB. The performance test environment must contain the bottleneck component but other components may not need to be representative of a full sized environment.

Modelling – This examines the use of modelling to take results from a small scale environment and predict the results for a larger scale environment.

Flipping – This looks at creating test environment that can be have the correct amount of resources allocated to them for a “full scale” performance test for example during off hours and then revert to a smaller scale performance test environment at other times.

Full Scale – Finally the advantages and disadvantages of a full scale performance test environment are discussed.

Finally the caveat for these techniques is that for any testing on a small scale performance test environment does not guarantee that all performance problems will be discovered due to application/scalability constrains that may only appear in the full sized environment!

You can download the presentation from here.