What Is Synchronization?

Applies To: System Center Data Protection Manager 2007

Synchronization is the process by which Data Protection Manager (DPM) transfers data changes from a protected computer to a DPM server and then applies the changes to the replica of the protected data. DPM relies on synchronization to keep replicas synchronized with the data on the protected computers.

Synchronization Frequency

You can select a synchronization frequency interval of anywhere from 15 minutes to 24 hours. The default is 15 minutes. You can also select to synchronize only before a recovery point is created. If you are protecting data that changes frequently throughout the day, you might want to synchronize your data every 15 minutes. If you are protecting data that changes less frequently, you can schedule fewer recovery points and synchronize your data only before each recovery point is made. For more information, see How to Modify Protection Options.

Synchronization Modes

DPM provides the following methods for synchronizing a replica:

• Incremental synchronization

• Synchronization with consistency check

Incremental synchronization (also referred to as synchronization) transfers changes to data from the protected computer to the DPM server and then applies the changes to the replica. When you create a protection group, you specify a synchronization schedule or accept the default schedule. In general, you can rely on incremental synchronization to keep a replica consistent with its data sources. This method is faster and more efficient than performing a consistency check because only data changes since the last synchronization are transferred and applied to the replica.

Synchronization with consistency check (also referred to as a consistency check) transfers the data changes from the protected computer to the DPM server but also performs block-by-block verification to ensure that all the data on the replica is consistent with the protected data. This process is slower than synchronization because all the data on the replica is compared rather than simply applying the data changes to the replica. A consistency check impacts the performance of both the protected computer and the DPM server to varying degrees, depending on network load, CPU processing power, and timing. If you schedule a daily consistency check, you should schedule it when other network traffic is low.

DPM automatically initiates a consistency check as a daily task if you have scheduled a daily consistency check for a protection group. DPM will also initiate a consistency check if you create a protection group, stop protection of that group with a "Retain data" option, and then re-protect the same data.

Because of the processing load imposed on both the DPM server and the protected computer, you should perform a manual consistency check only when it is necessary to make a replica consistent with its data sources. For example, this could happen when the change journal runs out of disk space or when a protected computer is shut down unexpectedly during synchronization.

Change Journal

A change journal is a Windows feature that tracks changes to NTFS volumes, including additions, deletions, and modifications. The change journal exists on the volume as a sparse file.

You can increase but not decrease the allocated disk space for the change journal, as needed.

See Also

Tasks

How to Synchronize a Replica

Concepts

Replica inconsistent
Synchronization failures
What Is a Consistency Check?
What Is a Recovery Point?
What Is a Replica?