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# Thread: Capacity vs Volume and Reliability vs Robustness

1. ## Capacity vs Volume and Reliability vs Robustness

Hi, All

I, as a non-native speaker, don't often fill a difference between meanings of close words. In context of performance testing I can't understand a difference between lines “Capacity and Volume”, and “Reliability and Robustness” in "Performance test types/Risks" matrix in the book ”Performance Testing Guidance for Web Applications”
http://perftestingguide.codeplex.com/wik...rringTitle=Home
Could somebody explain what is behind “capacity” risk and “volume” risk and what is difference between them? And the same question for “Reliability” and “Robustness”

Thanks,
Alexander

2. ## Re: Capacity vs Volume and Reliability vs Robustness

I tend to use those terms interchangeably. The document you cite treats them pretty much the same, as evidenced in some of the tables.

Someone else may have a different opinion.

3. ## Re: Capacity vs Volume and Reliability vs Robustness

Volume = the magnitude of work
Capacity = the potential to do work (measured in units of volume/time)

To tie these two terms together one might say that sufficient capacity is required to properly service a given volume.

As far as I know, Reliability = robustness, but I'm a performance guy so what do I know [img]/images/graemlins/smile.gif[/img]

4. ## Re: Capacity vs Volume and Reliability vs Robustness

I agree with Bernie re capacity/volume definition.

Reliability is often measured in terms of continuous time in operation. So a stress test - e.g. running tests over and over at a high load factor for several days - may be used to gauge reliability.

Robustness often refers to correct operation under all situations. For example, exhaustive edge case testing that yields proper handling of all conditions thrown at your software with no errors or crashes, may prove evidence of robustness.

Having said that, I've seen the above two terms used in exactly the opposite way. The software industry is pretty loose with terminology.

Good luck.

5. ## Re: Capacity vs Volume and Reliability vs Robustness

On reliability versus robustness.

I always like that say that reliability is relative and robustness is absolute.

So a non-robust system (one that will fall over when taxed heavily) can be perceived as reliable when it is never pushed to the limit. (That's why over-engineering can be a dangerous practice giving a a false sense of safety if you never figure out how robust your system is.)

A robust system is automatically reliable.
A reliable system is not automatically robust.

BTW, Robustness is the ability of a system to take a licking and keep on ticking.

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