Exchange 2007 is bringing major change to the Exchange messaging world, including in the area of availability. How many of you have either deployed, or attempted to deploy, Exchange 2000/2003 in a clustered configuration with the hopes that this scenario would provide a higher level of availability? I doubt there are many Exchange administrators out there that haven't at least considered this scenario. When set up and working perfectly properly, an Exchange cluster can actually provide a significant benefit.
But, there is a down side.
Exchange 2003 clustering is hard. And it doesn't always work out so well. In my organization, during our initial Exchange 2003 deployment, we ultimately gave up on clustering when it failed in our tests, leaving the mailbox data in an unrecoverable state. That kind of result doesn't exactly give you the warm fuzzies. And, I know I'm not alone. I've talked to a good number of colleagues at other institutions who either regret their clustered Exchange environment, or who have gone back to the single-server scenario. OK, to be fair, many of you are using clustering and are perfectly happy... it's just not for everyone.
Exchange 2007 aims to correct this.
Remember that Exchange 2007 is broken down into roles. One of those roles, the Mailbox Server role, is responsible for handling access to the Information Store. Under Exchange 2007, only this role can be clustered.
Exchange 2007 also provides a feature known as "Cluster Continuous Replication," which provides a hot backup of your Exchange database, providing you with a zero-point-of-failure, no-downtime setup if one of your Exchange servers fails. Under Exchange 2007, cluster continuous replication provides you with the following benefits:
- No single point of failure. Uses a fully replicated active/passive cluster that does not require shared storage, which was one of the most significant drawbacks to Exchange 2003's clustering implementation.
- Failover improvements: The CCR architecture means that recovery efforts cannot be hampered by a single problem, such as the failure of shared storage. Thus, incidents of problematic recovery should be reduced.
- Simplification: Since shared storage is not required, you can use any certified Windows server for your Exchange cluster. Previously, you had to choose servers that Microsoft supported for clustering. Further, Microsoft has streamlined the clustering installation, making is much easier to accomplish.
For high availability, it's hard to beat clustering and, in Exchange 2007, Microsoft appears to have made strides in this area.