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 recovery servers. SCR extends the existing continuous replication features and enables new data availability scenarios for Exchange 2007 Mailbox servers. SCR uses the same log shipping and replay technology as local continuous replication (LCR) and cluster continuous replication (CCR) to provide added deployment options and configurations. SCR is very similar to LCR and CCR, but it has unique characteristics of its own:
SCR enables a separation of high availability (comprised of service and data availability) and site resilience. For example, SCR can be combined with CCR to replicate storage groups locally in a primary datacenter (using CCR for high availability) and remotely in a secondary or backup datacenter (using SCR for site resilience). The secondary datacenter could contain a passive node in a failover cluster that hosts the SCR targets. This type of cluster would be called a standby cluster because it does not contain any clustered mailbox servers, but it can be quickly provisioned with a replacement clustered mailbox server in a recovery scenario. If the primary datacenter fails or is otherwise lost, the SCR targets hosted in this standby cluster can be quickly activated:
SCR Sources and Targets
As with LCR and CCR, SCR uses the concept of active and passive copies of a storage group, and like CCR, SCR requires that the database and log files paths be the same on the source and the target. Because SCR extends the scenarios supported by LCR and CCR, SCR also introduces the concepts of sources and targets.
The starting point for SCR is called the source, which is any storage group, except a recovery storage group, on any of the following:
As with LCR and CCR, SCR-enabled storage groups cannot contain more than one database; you cannot enable SCR for a storage group that contains more than one database, and you cannot add a second or subsequent database to an SCR-enabled storage group.
The endpoint for SCR is called the target, and the target can be one of the following:
A source can have multiple targets. For example, a source could have one target that exists in the same datacenter as the source, and a second target that exists in a separate datacenter. There is no limit to the number of targets you can have for each source; however, we recommend using no more than four targets per source. Impact to the source server needs to be verified and planned for accordingly if more than four targets are configured.
Requirements for SCR Targets
Target machines must be in the same Active Directory domain, but they can be located in the same or in different Active Directory Sites.
Each target can have multiple source servers. Both the source and the target system must be running Service Pack 1 for Exchange 2007. The operating system can be any operating system supported by Service Pack 1 for Exchange 2007.The database and log file paths on the source and all of its targets must match for each storage group being replicated with SCR. If both paths, including drive letter(s), do not match, you will not be able to enable SCR.
When a node or a server is configured as an SCR target these capabilities are blocked:
In my next blog entry, I'll talk about SCR target activation, as well as the cmdlets and processes used to set up, configure, and monitor SCR.
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