Synchronization of Replicas

Published : April 8, 2005 | Updated : August 17, 2005

In a process known as synchronization, each replica on the DPM server is regularly updated with changes made to the data sources, as shown in Figure 1.6. Through the protection group configuration, you can either schedule hourly (“near-continuous”) synchronization, or you can specify particular times for synchronization. You can also manually initiate synchronization at any time.

Figure 1.6   During synchronization, the replica is updated with changes to protected data

Between synchronizations, the DPM File Agent on the protected file server records changes to the protected data sources in a synchronization log on each protected volume. During synchronization, these changes are transferred to a transfer log on the DPM server, and then applied to the replica to synchronize the replica with the data sources. Figure 1.7 illustrates this process.

Figure 1.7   Incremental changes are stored on the protected file server, and then transferred to the DPM server and applied to the replica

Reliable data protection depends upon keeping each replica on the DPM server consistent with its protected data sources. If a replica becomes inconsistent with its data sources, DPM generates an alert that specifies which server and which data sources are affected. To resolve the problem, the administrator repairs the replica by initiating a synchronization with consistency check, also known as simply a “consistency check,” on the replica. During a consistency check, DPM performs a block-by-block verification and repairs the replica to bring it back into consistency with the data sources.

A consistency check is performed on each new replica before data protection begins for the protected volume. You can also schedule a daily consistency check for protection groups. A scheduled daily consistency check first determines whether the replica is inconsistent with its data sources. If the replica is inconsistent, a full block-by-block verification is performed, and the replica is repaired. If the replica is found to be consistent, no action is taken.