Microsoft's corporate bloggers have warned that using VMware's High Availability with Exchange 2010's database availability groups is unsupported and could increase cost and complexity for users. But IT pros that have virtualized Exchange dub these statements as posturing on the part of Microsoft.
The spat began when, earlier this month, VMware issued a white paper explaining how its High Availability (HA) feature can be used alongside Exchange 2010's database availability groups (DAGs) for application high availability and disaster recovery. The Microsoft Exchange Team blog took umbrage, calling VMware's guidance "reckless." It said further that the guidance "puts Exchange customers at risk," and that "combining these HA solutions will result in new storage requirements that increase cost and complexity."
The back and forth between the two vendors drew plenty of attention from the virtualization community, much of which was critical of Microsoft. Whether users deploy DAGs, VMware HA or both, most say they haven't heard exactly why the features won't work together or a specific scenario in which the use of DAGs with VMware HA would put their data at risk.
What's the DAG hangup?
A replacement for Exchange 2007's separate local and remote replication features, DAGs help perform mailbox and database-level failover, consolidate multiple cluster services into a single management console, and automate failover operations. VMware's HA works at the server level and when a physical node in an ESX cluster fails, it automatically restarts a virtual guest on another physical host.
DAGs and VMware features that perform automated live migrations, such as the Distributed Resource Scheduler (DRS) feature could potentially conflict, said Matt Liebowitz, a solutions architect at Kraft & Kennedy Inc., a Manhattan-based Microsoft and VMware channel partner that services law firms. VMware's vMotion requires at least a few moments of downtime before a guest machine goes live on a hew host and if a DAG service at the application level loses a "ping" while the guest is migrating, it could trigger an unnecessary application failover. "I've seen it happen [with DRS and DAGs] in a couple of instances," Liebowitz said.
But Liebowitz said the concerns with DRS don't apply with HA. "There's no online move with HA," Liebowitz said. "The server just restarts automatically, like any other Microsoft cluster node, and the DAG node can say, 'Hey, that server's back up again.' "
Since DAGs can be used with direct-attached or JBOD storage, Microsoft is theoretically correct when it asserts that using VMware HA, which requires networked storage, could result in higher storage costs for users. But in practice, most enterprises have network-attached storage or a storage area network anyway. Microsoft also counts as a strike against VMware that HA can't detect application-level outages, "but that's what you would also have a DAG for," Liebowitz said. Nobody wants the liability of violating a formal support statement, but "it's a silly restriction," he concludes.
Users must choose between features and support
Despite the lack of clarity on the problems that may result from using DAGs with VMware HA, none of the dozen or so Exchange 2010/vSphere installations Kraft & Kennedy has performed this year for law firms has involved VMware HA. And Liebowitz said it's because of Microsoft's support policy. "Email is such an important application for law firms, and it's not worth it to them not to have Microsoft's support if something goes wrong." Liebowitz said.
Exchange database availability groups and VMware features that perform automated live migrations could conflict.
Microsoft has the right to set its own best practices for applications, said Anthony LaSorsa, a systems engineer for Measured Progress, a Dover, N.H.-based education assessment firm. But LaSorsa has witnessed firsthand a Microsoft and VMware tussle over an unsupported Exchange configuration that ultimately worked just fine. "I had to jump through hoops to make sure my virtualized Exchange 2007 system would be supported," LaSorsa said. "All in all, I do think [this] is a wee bit of posturing on Microsoft's part here."
In the meantime, many users have forged ahead with DAGs and HA -- much like their counterparts that have virtualized Oracle on VMware vSphere despite similar formal support restrictions. "I appreciate a clearly defined support matrix," said Thad Vaughn, the assistant manager of technology infrastructure for Joyce Meyer Ministries. "However, I see this as another way that Microsoft is working to prevent their customers from using a competitor's product to its full value. … I fully intend on running Exchange 2010 DAGs on top of HA-backed VMware."
Users shouldn't hold their breath waiting for accord between the two vendors, according to Wikibon analyst Stu Miniman. As they have begun to do already, "customers that want virtualization, VMware, Hyper-V or otherwise [in Exchange environments] should drive this point back to Microsoft."
Beth Pariseau is a senior news writer for SearchServerVirtualization.com. Write to her at firstname.lastname@example.org.