There is no 'perfect' answer here.  There's what works best for your situation.   If you wish to leverage the ASM/ME features, and most do, then you must use the MS iSCSI initiator inside the guest OS to connect to the data and log volumes.   VMFS or RDMs won't work .  A key feature with Exchange integration is the exchange admin can w/o access to the EQL GUI, create a Recovery Storage Group and restore individual mailboxes on the fly from a snapshot.  It's managed entirely from the ASM/ME GUI.   You can also schedule consistent snapshots to be verified with ESEUTIL on another node, freeing up the Exchange server.   These are just a sample of the ASM/ME features.   Additionally, for best performance you would have different NICs for VMware iSCSI and the guest iSCSI traffic.    Regards,  -don 
Hi Everyone, I'm just in the planning stages of a Exchange 2010 deployment (upgrade from 03). Although I've attended a fair amount of EQL webinars on exchange and read probably every best practice doc out there, I can't seem to get a straight answer about a fairly major point - how best to host the storage.  This will be a relatively small exchange deployment (500 mailboxes, 1 PS4000XV, 2 Dell R910's on vSphere 5). I can't seem to find any consensus on how to host the storage. What I'm talking about is either do you A) Make the exchange data volume a simple VMDK disk (within a VMFS volume on the EQL), or B) Make the exchange data volume sit directly on the SAN (i.e. RDM or iSCSI Target, so that the exchange data is not inside VMFS). Everything I'm reading seems to say that the ASM/ME tools need to be able to talk to the volume directly on the SAN, making option B the one to go with. I know there could be advantages and disadvantages to both, so perhaps one option isn't a slam dunk, but are there any opinions out there on the matter? Any best practices?  
Exchange 2010 on EqualLogic - VMFS volume?