Whilst at VMworld Europe 2010 I attended a session on virtualising Exchange 2010. This was one of the most useful sessions I went to and whilst it confirmed a number of issues I had read about in the Best Practices Guide there was one tip I picked up from the session that was not in the guide and I thought would be useful to share.
When deploying Exchange 2010 in a Database Availability Group (DAG) on vSphere the Database and Log file disks are only currently supported on RDM disks not VMFS.
On my return to the UK I confirmed this with VMware via a support call
The supported method of deploying Exchange 2010 DAG at the moment is by having the Exchange database and log files deployed on RDM disks. DAG has not completed the QA process for VMFS volumes which why we are not recommending VMFS for DAG storage at the moment.
We do have some customers that have Exchange DAG supported on VMFS but they needed to have their configuration approved using the RPQ process. A RPQ is an exception that allows a currently unsupported configuration to be supported once the conditions of the RPQ process are met. You would need to engage with your VMware Account Manager to initiate the this process if you want to go down this route.
Hopefully I will find out when VMFS support arrives and can update this post.