Dell PowerVault DP600 - Manual (Page 20)

20
The Application Data Synchronization
Process
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