Standby continuous replication (SCR) is a new feature being introduced in Service Pack 1 for Microsoft Exchange Server 2007. As its name implies, SCR is designed for scenarios that use standby reco...
Updated Jul 01, 2019
Version 2.0
Blog Post
Brian: When you install Exchange 2007 into a Windows failover cluster, there are two roles that can be installed: one is the Mailbox server role, and the other is the Active Clustered Mailbox Server (CMS) role. Only the Active node gets both roles installed. The passive node only gets the Mailbox role installed. Thus, a CMS is always and only created and only exists on the Active node. Note, though, that this does not prevent a Passive node from becoming an Active node, and you don't need to install the CMS role on a Passive node. This role distinction is only so Setup can install the role you want to install (e.g., Active vs. Passive).
So what we're saying with an SCR target is that you can only have the Passive role (e.g., only the Mailbox role) installed. You cannot have a CMS in the cluster. If you imagine a two-node cluster then, basically what you're doing is installing the Passive role on both nodes. You don't install the Active role because a failover cluster that is configured as an SCR target cannot contain a CMS.
So what we're saying with an SCR target is that you can only have the Passive role (e.g., only the Mailbox role) installed. You cannot have a CMS in the cluster. If you imagine a two-node cluster then, basically what you're doing is installing the Passive role on both nodes. You don't install the Active role because a failover cluster that is configured as an SCR target cannot contain a CMS.