Difference between LCR, CCR and SCR in Exchange Server 2007

LCR	CCR	SCR
Support only one target passive copy	Support only one target passive copy	Supports multiple targets per storage groups
Can backup LCR Copy	Can backup CCR copy	Cannot backup SCR copy
Log shipping is Continuous and uses a PULL model	Log shipping is Continuous and uses a PULL model	Log shipping is Continuous and uses a PULL model
Does no use Windows Clustering	Uses Windows Clustering	Uses Windows Clustering
Double Storage requirements	Double Storage requirements	Single Storage requirements

 Cluster Continuous Replication is one on the new highly availability feature in Exchange Server 2007. This new feature uses Log file shipping and replay technology with failover feature provided by the Cluster service.

As you know in traditional cluster node approach, Active/passive model was used where nodes were sharing common database, called as quorum. But this model has one major drawback, which was single point of failure of Exchange databases

CCR in Exchange Server 2007 has overcome this limitation by providing no single point of failure without any shared storage requirements. Also, no special hardware is required to implement this model.

When we create a passive node, a copy of storage group and database is copied from active to passive node, and this process is called Seeding. After initial seeding, log copying and reply is performed continuously.

One important thing to note down is logs are copied only when they are closed and Mailbox server is not using them. This means passive node will not be having all the copies of log files that exist on active node.