Have had this discussion on many occasions and this 3Sharp whitepaper by Missy Koslosky would have proved very useful as an external reference point… High Availability Choices for Exchange Server 2007: Continuous Cluster Replication or Single Copy Clustering In conclusion…  (this isn’t the only bit I read) “Exchange Server 2007 is a mission critical application. Organizations rely on the services and data Exchange provides, and keeping these highly available is of the utmost importance. Native, application-specific data replication functionality is the proper solution to meet the needs of these organizations. There are several options within Exchange Server 2007 that provide failover and high availability services, and among these, CCR provides the most highly available, cost-effective solution to achieve low RTO and RPO while reducing costs and complexity. SCC offers an incomplete solution; its fatal flaw is the lack of multiple database copies. Although multiple servers may be involved in an SCC cluster, if a problem occurs with a mailbox database, there is no alternate copy of the database without the use of costly and complicated additional products, requiring disaster recovery operations to be performed to restore service to users, and resulting in an unacceptable RTO/RPO. CCR is a robust clustering solution that provides true high availability services for organizations. CCR is easier to implement, easier to manage and maintain, and provides better availability all at a lower cost, while allowing organizations to satisfy the needs of their users by deploying large mailbox quotas.” If you’re considering SAN , synchronous replication and SCC over DAS , asynchronous replication and CCR I’d recommend reading this whitepaper…...(read more)