A new feature in Exchange 2010. Its name is Database Abailability Group (DAG in the future) and its called to substitute Exchange 2007 's CCR and SCR. While still using the same technology to replicate and replay database logs among servers, this new technology allows to provide database high availability to database level. It's important to say that in Exchange 2010 the concept of Storage Group disappears: Exchange just manages plain databases.
Once you create a DAG and add mailbox servers, you can configure each single database to replicate to the desired servers inside the DAG. If the server in which a database is mounted fails or an administrator swith it over to another server in the DAG, then another server in the DAG will activate and mount the database, depending on the database configuration.
In order to provide this features, Exchange 2010 relays in a new component called Active Manager. This component abstracts the availability feature from Windows Failover Cluster. Although Active Manager depends on Failover Cluster service for some networking features, it does not in the storage management features. This independency from Failover Cluster storage architecture allows to simplify Exchange servers' storage system. In order to configure DAG, Failover Cluster feature must be installed on every DAG node, and a File Share Witness external to any node in the cluster will have to be provided.
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