Diagnosing I/O wait issues

• when diagnosing a slow system, one of the first things you should look at is the I/O wait so you can rule out disk I/O.

• if I/O wait is low, you can look at the idle percentage.

• if I/O wait and idle are low, then you will likely see a high user time percentage, so you must diagnose what is causing high user time.

• if the I/O wait is low and the idle percentage high, then you know any sluggishness is not because of cpu resource, and you will have to start troubleshooting elsewhere. this might be network problems or slow queries in mysql.