Today, just before TechNet North America 2011, Microsoft published a whitepaper on virtualizing Exchange 2010, “Best Practices for Virtualizing Exchange Server 2010 with Windows Server® 2008 R2 Hyper V“.

There are some interesting statements in this document which I’d like to share with you, also after the Exchange team published an article on supported scenarios regarding virtualized shortly shortly after this paper was published.

First, as Exchange fellow Steve Goodman blogged about, a virtualized Exchange 2010 SP1 UM server role is now supported, albeit under certain conditions. More information on this at Steve’s blog here.

The second thing is that live migration, or any form of live migration offered by products validated through the Windows Server Virtualization Program (SVVP) program, is now supported for Exchange 2010 SP1 Database Availability Groups. Until recently, the support statement for DAGs and virtualization was:

“Microsoft does not support combining Exchange high availability (DAGs) with hypervisor-based clustering, high availability, or migration solutions that will move or automatically failover mailbox servers that are members of a DAG between clustered root servers. DAGs are supported in hardware virtualization environments provided that the virtualization environment doesn’t employ clustered root servers, or the clustered root servers have been configured to never failover or automatically move mailbox servers that are members of a DAG to another root server.”

The Microsoft document on virtualizing Exchange Server 2010 states the following on page 29:

“Exchange server virtual machines, including Exchange Mailbox virtual machines that are part of a Database Availability Group (DAG), can be combined with host-based failover clustering and migration technology as long as the virtual machines are configured such that they will not save and restore state on disk when moved or taken offline. All failover activity must result in a cold start when the virtual machine is activated on the target node. All planned migration must either result in shut down and a cold start or an online migration that utilizes a technology such as Hyper-V live migration.”

The first option, shutdown and cold start,  is what Microsoft used to recommend for DAGs in VMWare HA/DRS configurations, i.e. perform an “online migration” (e.g. vMotion) of a shut down virtual machine. I blogged about this some weeks ago here since VMWare wasn’t always clear about this. Depending on your configuration, this might not be a satisfying solution when availability is a concern.

The online migration statement is new as well as the host-based fail-over clustering. In addition, though the paper is aimed at virtualization solutions based on Hyper-V R2, the Exchange Team article is more clear on supported scenarios for Exchange 2010 SP1 with regards to 3rd party products (VMware HA); if the product is supported through the SVVP program, usage of Exchange DAGs are supported. Great news for environments running or considering virtualizing their Exchange components.

Be advised that in addition to the Exchange team article, the paper states the following additional requirements and recommendations as best practice:

• Exchange Server 2010 SP1;
• Use Cluster Shared Volumes (CSV) to minimize offline time;
• The DAG node will be evicted when offline time exceeds 5 seconds. If required, increase the heartbeat timeout to maximum 10 seconds;
• Implementation of latest patches for the hypervisor;
• For live migration network:
  – Enable jumbo frames and make sure network components support it;
  – Change receive buffers to 8192;
  – Maximize bandwidth.

Note that on May 17th the DAG support statement for Exchange 2010 SP1 on TechNet was updated to reflect this. However, the last two sentences might restart those “are we supported” discussions again:

“Hypervisor migration of virtual machines is supported by the hypervisor vendor; therefore, you must ensure that your hypervisor vendor has tested and supports migration of Exchange virtual machines. Microsoft supports Hyper-V Live Migration of these virtual machines.”

So, if vendor A, e.g. VMWare, has tested and supports vMotioning DAGs with their hypervisor X, Microsoft will support Live Migration for virtual machines on hypervizor X using Hyper-V? Now what kind of statement is that?

(Updates: May 16th – statements from EHLO blog, May 17th – mention updated TechNet article)