For application data, after the replica is created by DPM, changes to volume blocks that belong to application files are tracked by the volume filter.
How changes are transferred to the DPM server depends on the application and the type of synchronization. The operation that is labeled synchronization in DPM Administrator Console is analogous to an incremental backup, and it creates an accurate reflection of the application data when combined with the replica.
During the type of synchronization that is labeled express full backup in DPM Administrator Console, a full Volume Shadow Copy Service (VSS) snapshot is created but only changed blocks are transferred to the DPM server.
Each express full backup creates a recovery point for application data. If the application supports incremental backups, each synchronization also creates a recovery point. The synchronization type supported by each type of application data is summarized as follows:
- For protected Exchange data, synchronization
transfers an incremental VSS snapshot using the Exchange VSS
writer. Recovery points are created for each synchronization and
express full backup.
- SQL Server databases that are log-shipped, in
read-only mode, or that use the simple recovery model do not
support incremental backup. Recovery points are created for each
express full backup only. For all other SQL Server databases,
synchronization transfers a transaction log backup, and recovery
points are created for each incremental synchronization and express
full backup. The transaction log is a serial record of all the
transactions that have been performed against the database since
the transaction log was last backed up.
- Windows SharePoint Services and Microsoft
Virtual Server do not support incremental backup. Recovery points
are created for each express full backup only.
Incremental synchronizations require less time than performing an express full backup. However, the time required to recover data increases as the number of synchronizations increases. This is because DPM must restore the last full backup and then restore and apply all the incremental synchronizations up to the point in time selected for recovery.
To enable faster recovery time, DPM regularly performs an express full backup, a type of synchronization that updates the replica to include the changed blocks.
During the express full backup, DPM takes a snapshot of the replica before updating the replica with the changed blocks. To enable more frequent recovery point objectives, as well as to reduce the data loss window, DPM also performs incremental synchronizations in the time between two express full backups.
As with the protection of file data, if a replica becomes inconsistent with its data source, DPM generates an alert that specifies which server and which data source are affected. To resolve the problem, the administrator repairs the replica by initiating a synchronization with 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.
You can schedule a daily consistency check for protection groups or initiate a consistency check manually.