Which Exchange Server 2007 Server Cluster Type Should I use, CCR or SCC?

This is becoming a pretty common question in my Exchange classes. Which should I use? Why one over the other?


My current recommendation is to use CCR whenever possible vs. SCC. Why? I am glad you asked that question.


High Availability, see my definition here, is all about risk mitigation. What we should be doing is identifying risks to our important/critical applications and finding ways to eliminate or at least mitigate the risks where economically feasible.


One of the major risks that I see with Exchange Server 2007, as well as previous versions of Exchange, is losing my production database because of a disk failure or my database becoming corrupted. In the case of a disk failure, I would normally restore my database, but that takes time, and very few people want to run a dial tone database while they recover. So, two Exchange Server 2007 technologies provide some protection against a lost database drive or a corrupted database. One is Local Continuous Replication (LCR). LCR, however, is a single server technology and does not provide the risk mitigation against an entire server loss that a cluster can provide. The second technology is to use Cluster Continuous Replication (CCR). CCR provides the one extra piece that a Single Copy Cluster (SCC) does not: it provides for loss of the database disk or corruption of the database.


Since CCR does not do a block by block copy like a SAN replication utility might, the likelihood of corruption passing from the production database to the passive copy is extremely low. Remember, the passive copy is receiving transactions and having them applied to the database much like the production database. Corruption is not copied in such an environment.


Of course, we can’t forget that by using CCR, we also can eliminate the need for a SAN, which is a huge cost savings.


So, add the increased risk mitigation and elimination of the SAN requirement for high availability and you can see that CCR is a vast improvement over SCC.

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