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Plan for disk-based backups

Updated: August 13, 2014

Applies To: System Center 2012 - Data Protection Manager, System Center 2012 R2 Data Protection Manager, System Center 2012 SP1 - Data Protection Manager

DPM provides short-term backup to disk by saving data to the DPM storage pool. The storage pool is a set of disks or volume that you configure during DPM deployment. For more details, see Plan the storage pool.

Synchronizing data to disk

Data replicated from protected resources is stored in the storage pool. DPM creates recovery points (snapshots) of this replicated data. DPM keeps replicated data synchronized by transferring data changes from the source to the DPM server, and then applying those data changes to the replica in the storage pool. DPM does this with:

  • Incremental synchronization—DPM checks what’s changed on the data source and updates the delta changes on the replica.

  • Incremental synchronization with consistency check—DPM checks what’s changed on the data source and updates the delta changes on the replica with an additional block-level check of the replica to ensure data consistency.

DPM handles this synchronization slightly differently depending on whether file or application data is being replicated.

Synchronizing file data

  • For file-based resources (volumes, shares, folders) the DPM protection agent uses a volume filter and the change journal to figure out which files have changed, and then performs a checksum procedure for these files to synchronize only the changed blocks. The changes are transferred to the DPM server and applied to the replica to synchronize it, as shown.

    How file changes are synchronized
  • If a replica becomes inconsistent DPM generates an alert. To resolve it the administrator repairs the replica by initiating synchronization with a consistency check on the replica. DPM performs a block-by-block verification and repairs the replica to bring it back into consistency with the data source.

  • You can schedule a daily consistency check for protection groups or initiate a consistency check manually.

  • At regular intervals you can configure, DPM creates a recovery point for a protection group member. A recovery point is a version of the data from which data can be recovered. For files, a recovery point consists of a shadow copy of the replica, which is created by using the Volume Shadow Copy Service (VSS) functionality of the operating system on the DPM server.

Synchronizing application data

  • 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:

    • Synchronizations labelled synchronization in the DPM Administrator Console are basically an incremental backup. When combined with the replica it creates an accurate reflection of the application data..

    • Synchronizations labeled express full backup in DPM Administrator Console indicate that 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.

    • Workloads use the following types of synchronization:

The synchronization type supported by each type of application data is summarized as follows:

  • Exchange—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.

  • SharePoint—Doesn’t support incremental backup. Recovery points are created for each express full backup only.

Comparing incremental and full express backup

  • 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.

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For additional resources, see Information and Support for System Center 2012.

Tip: Use this query to find online documentation in the TechNet Library for System Center 2012. For instructions and examples, see Search the System Center 2012 Documentation Library.
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