Standby continuous replication (SCR) is a new feature introduced in Microsoft Exchange Server 2007 Service Pack 1 (SP1). As its name implies, SCR is designed for scenarios that use or enable the use of standby recovery servers.
As with LCR and CCR, SCR uses the concept of active and passive copies of a storage group, but instead refers to them as sources and targets. Also, as with CCR, SCR requires that the database and log file paths be the same on the source and the target.
SCR uses the same Replication technology used by CCR and LCR but in a different way. Using SCR we have the concept of Source (Active copy) and Target (Passive Copy) and they have some requirements, as follows:
The Operating System used by target and source must be the same.
Exchange Server 2007 SP1 must be installed in both: Source and Target.
They must be in the same Active Directory domain.
The target can handle 50 Storage Groups in the Enterprise Edition and 5 Storage Groups in the Standard Edition.
The target must have at least the Mailbox Server role installed.
In the target server there is no indication of the replication using Exchange Management Console.
The database and storage group paths must be the same in the source and target; this means that the paths must be defined cautiously. Example: two sources cannot use the same path for database and storage groups with a single target.
The Replication service will maintain the database, log files and path in the target SCR, it is not necessary to create a folder or anything else before enabling it.
One source can have multiple targets; one target can have multiple sources.
Microsoft recommends no more than 4 (four) targets per source.
One last thing to mote before starting to play with SCR, we cannot back up a SCR target only the SCR source.