Ubuntu huge iowait on Vmware 4.1

I spent many hours search web and forums for this solution.

I tried almost everything I saw, but no success.

I have a vmware cluster, 3 powerful hosts and fiber based storage solution from HP. Have around 50 VMs running.

All Windows guests OS runs fine, but the Linux have a huge iowait. I used Ubuntu 12.04 and 10.04. Both very slow disk write time.

I dont know what to do now.

Please, any tips...