Lagged Copies

In Exchange Server 2007 you can configure a Standby Continous Replication (SCR) server. This an Exchange Server that will hold an additional copy of the Mailbox Database. This copy is not for a High Availability solution, but for a Disaster Recovery solution. It is possible on a SCR Server to configure a ´lagged copy´ of the Mailbox Database. A lagged copy is a copy of the Mailbox Database that has a certain lag time, this copy is a certain amount of time behind the production server. The log files are copied to the SCR Server immediately, but they are replayed into the Mailbox Database only after a specific, configurabel time. This is called the lag time.

In Exchange Server 2010 you can configure a Database Availability Group (DAG), and a Database Availability Group can also hold a lagged copy. The lag time in the DAG can be up to 14 days. In this case the log files are copied from the Active Database to the passive Database, but they are replayed into the Database only after 14 days. Needless to say you need quite an amount of disk space to accomodate 14 days of log files.

If you have a copy in a DAG, and you want to configure a lag time of 24 hours (1 day) on this copy, open the Exchange Management Shell and enter the following command:

Set-MailboxDatabaseCopy -Identity MBX01\SERVER02 -ReplayLagTime 1.0:0:0

It is also possible to create a copy a Mailbox Database and configure the lag time immediately. Open the Exchange Management Shell and enter the following command:

Add-MailboxDatabaseCopy -Identity MBX01 -MailboxServer SERVER02 -ReplayLagTime 1.0:00:00 -ActivationPreference 2

Please remember that a lagged copy is considered a Disaster Recovery solution and not a High Availability solution.


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