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What Is Synchronization?

Updated: April 21, 2010

Applies To: System Center Data Protection Manager 2010

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. 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 it uses the DPM filter to identify the changed blocks.

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 may be required when the DPM cannot track the changes to a protected data source. This can occur if the change journal runs out of disk space or when a protected computer is shut down unexpectedly during synchronization. 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 select the option to automatically perform consistency check if the replica is inconsistent or 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.

noteNote
DPM raises an alert if the change journal runs out of disk space or when a protected computer shuts down unexpectedly during synchronization. The alert indicates that the administrator should run a consistency check.

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. DPM uses the change journal to identify the set of files that have changed since the last synchronization when backing up file servers or client computers.

See Also

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