High CPU usage when Disk Queue is very high. (Domino + Windows)

A customer has one Domino cluster with 2 members on a virtualized environment (VMWare). it is not a big environment (1600 users) but after 3 months working well some thing happened and the system does not work well.

During a period of 4 hours (9 am to 13 pm) the CPU of one cluster member goes to 100% and the cluster does not send users to the another member.

I check everything possible (this server has 800 GB of mailboxes) and run some administrative commands.  I raise a PMR and sent NSD's.

IBM told me  that the windows kernel is consuming a lot of CPU and Domino was not the cause, but this machine only run Domino.

We talk a lot about the problem an after some verification at the windows 2012 level, we saw a high disk queue lengh (between 8 and 12).

The solution:   The VMWare administrator put each disk on different LUN (We have 3:  OS, Data and Tranlog).

 Until now the machine works well and the disk queue length is bellow 1,2