Why is iometer performance slower after first run

benchmarkiometerperformancevirtualization

I'm doing some benchmarking with IOMeter, and I'm seeing a consistent and susbtantial drop-off in performance after running the first test in my VMWare environments. These drop-offs are about the same on the three VMs I've tested on, which makes me think it's a configuration setting, or something about my VMs.

For example, one system (local RAID 10) went from 388 I/Os per second the first run, to about 211 I/Os per second on every run after that. Everything else about the test was identical, and I also bounced the machine in between runs. Testing on my local machine in a non-virtualized environment is consistent, whereas if I test it with a local VM, I also get a performance drop-off after the first run.

Any explanations or suggestions to explore?

Best Answer

Are you using the entire VM drive for the test? On a fresh VM when you run your test you are starting with no allocated data. There is nothing the test needs to delete to write. On your subsequent test, you are likely having to delete, then write, which is going to cause the second test to be slower.

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