It's a great solution, but make no mistake: There's a cost involved that may prove to be too much, based on your needs. Designing high availability properly, depending on your environment, will require multiple servers all running the Enterprise Edition of Windows Server 2008/R2.
Even if you use virtualization for your Exchange environment, you still need to make sure you don't place these virtualized servers on the same physical box. Otherwise, you're completely defeating the purpose of high availability. Some Exchange admins forget that fact and put multiple VMs on the same physical server. If that box goes down, they lose all VMs and all their Exchange availability.
When using DAG, you also need to worry about multiple LAN connections, multiple routing options, and even multiple WAN connections if you're working with cross-site replicas (necessary to provide site resiliency).
On the positive side, DAG works. And compared to many third-party options, the extra cost and effort of using Exchange's built-in DAG high availability on Windows Server Enterprise is often still the cheaper option.
But unless you set up your Exchange configuration properly to avoid issues such as split-brain syndrome, placement of all critical VMs on one server, and network routing dead ends, Exchange 2010's high-availability capabilities won't be able to do their job. It's thus essential to understand DAG design and make sure you have enough servers to take advantage of other built-in Exchange features like lagged mailbox database replica copies, retention policies, legal hold, and archiving.
As with aircraft, the systems are in place to prevent disaster and help recover from major shocks to the system. But as is the case with pilot error, admin error or lack of understanding can nullify all high-availabillity technology. Don't let it happen to you.
This article, "Make Exchange 2010 bulletproof with replication," was originally published at InfoWorld.com. Read more of J. Peter Bruzzese's Enterprise Windows blog and follow the latest developments in Windows at InfoWorld.com. For the latest business technology news, follow InfoWorld.com on Twitter.