why is iometer performance slower after first run?

Posted by Dan on Server Fault See other posts from Server Fault or by Dan
Published on 2010-06-03T20:48:19Z Indexed on 2010/06/03 20:56 UTC
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I'm doing some benchmarking with IOMeter, and I'm seeing a consistent and susbtantial drop-off in performance after running the first test. These drop-offs are about the same on the three systems I've tested on, which makes me think it's a configuration setting, or just a fact of life about using IOMeter.

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.

So, is this expected behavior, or am I missing something?

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