MySQL Read/Write Benchmark
You should use MySQL's BENCHMARK() function

Here are my posts on how to use it


Apr 03, 2012 : How to use the &#39;select benchmark&#39; command on a procedure
Apr 16, 2013 : MySQL: CAST + SUBSTR vs. FLOOR + MOD


BTW if you do configuartion changes, you should restart mysqld immediately after the configuration changes are in place. Then, run your I/O tests.