Hi all,
After an opened case and dozens of tests, I found these links, explaining this "weird" beahviour :
New disk IO scheduler used in vSphere 5.5
vSphere 5.5 and disk limits (mClock scheduler caveat)
In brief, the new disk IO scheduler introduced in vSphere 5.5 consider an I/O with a maximum of 32kb. If your IOs are bigger, when you specify an IO limitation, the calculation will be in multiples of 32KB... Please, read these links, Duncan explains it really well... Kudos to him !
I am just annoyed that VMWare don't communicate enough on these changes, as they are pretty big !
Regards,
Vincent.