At least some users say they will forge ahead with a combination of DAGs and VMware HA regardless of what the vendors think, saying they still see a combination of features as the best of both worlds.
VMware HA monitors the virtual machine (VM) and can trigger a restart on another node in an ESX cluster should there be a failure. DAGs, in the meantime, work at the application level and allow for Exchange database replication, to protect application data in the event of a failure and to trigger failover should a failure occur at the app level rather than in the VM.
The back-and-forth over Exchange high availability began last November, when Microsoft’s corporate bloggers warned that the use of VMware HA with Exchange 2010 DAGs is unsupported, could increase cost and complexity, and potentially put data at risk. But IT pros that have virtualized Exchange dubbed these statements as posturing from Redmond, and said that they haven't heard exactly why the features won't work together.
VMware strikes back
Now, VMware has returned fire with an architecture design proposal posted on its Business Critical Applications blog, which claims to eliminate the need for DAGs entirely. The post claims VMware’s new AppHA, currently supported through application programming interfaces by Symantec Corp. and other partners, adds an “application heartbeat” to the server-based heartbeat tracked by VMware HA. As for OS availability, “[users] could enable VM Monitoring to protect against guest OS failures by monitoring VMware Tools running within the virtual machine,” according to the post.
At least one channel partner who works with both vendors, and had wondered about Microsoft’s lack of support for VMware HA with DAGs, said he’s just as concerned about VMware’s suggestion, and that it only further muddies the waters.
“On the one hand, VMware wants to demonstrate the new capabilities of the new AppHA. In my opinion that's a huge step forward and really helps with the availability of applications that don't already have their own native high availability,” said Matt Liebowitz, a solutions architect at Kraft & Kennedy Inc., a Manhattan-based VAR that mainly serves law firms.
“On the other hand, VMware should be promoting that vSphere is capable of running tier 1 applications like Exchange 2010 using their full capabilities. Suggesting that customers shouldn't use the biggest single improvement to the Exchange platform -- Database Availability Groups -- in order to use VMware HA and still be supported seems to go against that,” he said.
Liebowitz also said in a blog post that he can see at least some use cases where VMware’s design could work well, including small environments, environments which have already invested in host- or storage array-based HA tools for Exchange, and environments that require vMotion on mailbox servers. But he wrote, “I personally cannot think of a use case where I would want to use vMotion over moving databases between nodes in a DAG.”
Segregated Exchange, VMware teams complicate matters
Another VMware user, Terry McMillan, an infrastructure systems analyst at a large utility in Canada, said the design still wouldn’t fly in his organization, simply because he’s not in charge of the Exchange environment -- a separation of duties not uncommon in medium to large enterprises.
Liebowitz said it’s often organizational issues like this, or simply wanting to stick with a supported configuration, that prevent Exchange 2010 virtualization in many of his clients’ environments.
Even if this were not the case, though, McMillan added, “I would not replace DAGs with third-party software for HA. I just wouldn’t want another layer of complexity with something as important as Exchange.”
At least some users, meanwhile, are still doggedly sidestepping this vendor food fight and pushing ahead with a combination of DAGs and HA, despite Microsoft’s lack of support and VMware’s suggestions to do otherwise.
“My stance is that if a feature makes sense to use and is the right thing to do, architecturally (and sometimes economics plays into the equation), then I would give more weight to that for decision-making,” said Hal Rottenberg, an author and vExpert who also manages vSphere for a midsized company. “If, at the end, we come up with something that's not supportable by the vendor, I would often just push ahead anyway.”
Rottenberg said he runs Exchange 2010 in an environment that’s almost 100% virtualized with vSphere. “I don't enable or disable HA based on the OS or software inside of a VM,” he added. “The customer isn't always right, but they are the ones with the money, so it usually works out.”
Some virtualization veterans see merit to both Microsoft’s and VMware’s approaches, but also said history is repeating itself when it comes to Microsoft support for VMware features.
“It seems [with]… capabilities such as 16 copies of the mailbox database that DAG has, that it would fit better in larger deployments,” said Shannon Snowden, a manager of delivery services at consulting firm New Age Technologies in Louisville, Ky. “Ultimately, I expect if the market is demanding it, just like they did with the operating system, Microsoft will eventually support the VMware HA configuration.”
Meanwhile, it remains unclear what deeper technical incompatibilities exist between Exchange 2010 DAGs and VMware HA that have prompted Microsoft’s lack of support.
Reached for comment on the issue, a Microsoft spokeswoman had no comment other than to say Exchange users should stay tuned for “virtualization news coming in a few months.”
Beth Pariseau is a senior news writer for SearchServerVirtualization.com. Write to her at firstname.lastname@example.org.