Here are some thoughts on VMware and Exchange:
Having researched this matter yesterday and this morning, it is clear that there are various decisions which could be taken.
1. Microsoft do not officially support Exchange 2007 on a virtualisation platform. Equally, they do not officially support their OS on non MS virtualisation platforms.
It is clear the MS do support Exchange 2003 on their own virtualisation platform (Virtual Server 2005).
Having spoken to various people internally at MS it seems highly likely that when the MS Viridian technology ships (within 180 days of Server 2008) Exchange 2007 SP1 will also be supported on a virtual platform.
It would seem that there are various pieces of anecdotal evidence out there on forums (see link below) which supports the statement that;
MS will very likely provide support for problems even if it is on virtual hardware, although there is a chance they will ask for the problem to be reproduced on physical hardware.
My suggestion would be to see what VMware?s support position is on Exchange 2007 and whether they will offer cover under their support model. Alternatively, if the implementation partner have a Premier Support Agreement (PSA) with MS then we may be escalate calls to MS where required as, having a PSA ensures that MS will make best effort to fix the problem without regard for the platform.
2. The next discussion point is around the various Exchange roles and which could/should be virtualised.
It would appear from various sources (see link below) that MS personnel are at least relatively happy with the idea of virtualising the non Database roles of Exchange 2007 using 3rd party virtualisation software.
I would agree with this in principle so long as being officially supported by MS is not a show stopper for the client. I feel that running the Exchange Mailbox server role on VMware would not make sense technically as the IO and Memory requirements would likely negate the benefits of the virtualisation platform, especially with the Exchange DR/Replication solutions now available natively in Exchange 2007.
Therefore, moving onto the non DB roles, it would appear to me that the final possible barrier to virtualising the non DB roles (Client Access and Hub Transport) would be the implementation of Windows Network Load Balancing (WNLB) on ESX server. From the links below, it would appear that this is perfectly possible:
In summary; where the client is not concerned about official support from MS, or where a partner, through a Premier Support Agreement, will proxy the support requests I would accept that virtualising the non DB Exchange roles is a viable proposition. I would only consider virtualising the whole of Exchange where the system is either not mission critical (i.e. it is acceptable for mail to not be available for a period whilst the system is rebuild on physical hardware) or where the number of users is very small i.e. less than 100.
I hope this helps lead discussion.