Cluster continuous replication

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Cluster Continuous Replication (CCR) is a mechanism that ensures high availability in the Microsoft Exchange 2007 software package.

This technology makes use of following features:

1. Majority Node Set(MNS) quorum
2. Log file shipping
3. File share witness

In Exchange 2007 server, by design only mailbox server role can be deployed in a clustered environment. In this Cluster model, each server node has it's own Quorum and database storage drives. In this model database copy of the active node is created and the logs are shipped to the passive node and committed to keep both the database up to date. In the event of failure of a service, the cluster services immediately failover to the passive node and continues serving new client requests allowing for minimal downtime, even in case of Corruption of live Exchange database files.

Since the cluster uses MNS quorum model, a third node is needed for the cluster to be alive. As in two node MNS cluster the whole cluster fails in case of failure of a single node. The need for the third node is taken care by the File share witness feature.

File share witness is a File share configured on any Windows server 2003 computer (though Microsoft recommends Hub role server) which counts for one vote in an MNS cluster to keep the cluster alive in case of failure of one node.

[edit] External links

• A Microsoft TechNet article that gives a detailed description of CCR.
• This KB article gives a detailed description of the File share witness and Exchange 2007 Technet library gives the technical information about the CCR.