How the Synthetic backup process works with changed data between the Full, Incremental and Synthetic backup stages.
Article ID: 100022764
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Advantage of Synthetic Full Backup:
Synthetic backup is also known as catalog driven backup because it maintains the table of catalog information and updates it with the help of the Collect additional information for synthetic backup feature, constantly depending upon the file appended, modified, or deleted. Due to this intelligence, it does not include the file which is deliberately deleted by the user and is no longer required during restore. In this condition, any NORMAL FULL backup job would restore the "Deleted File" whether you want it or not. But in the case of Synthetic Full backup, it excludes such files and does not include it in the final catalog information for the Synthetic Full Backup, which not only makes the restore job faster, but also compact.
It can be misunderstood the Normal Full backup (Baseline) will match the Synthetic Full backup once the Incremental backups are synthesized with the Baseline.
It is important to understand when the Synthetic backup synthesizes the Incremental backups, it then becomes a Full backup of the server at the time when the Synthetic was ran, not when the Baseline was initiated. Restore selections for Synthetics will appear to be missing information, when in fact, this is by design.
The ADBO option is intended to provide a reduced backup window as another FULL backup is not needed as the Incremental data has been synthesized into one Synthetic Full backup. It also provides reduced network traffic as the Synthetic backup job does not need to access the network.
Example:
How synthetic backup excludes the "deleted file" with the help of catalog driven backup:
1. The following files are selected for backup:
a. File A.txt
b. File B.txt
c. File C.txt
The Restore tab shows that all three files have been backed up.
Before running the Incremental backup, modify the following files:
d. Delete the file B.txt
e. Append the file C.txt
2. Running Incremental backups would result in the backup of C.txt and the catalog information will be updated about the deletion of B.txt file.
The figure below shows only C.txt has been backed up.
Now, run a Synthetic backup.
3. The Restore tab shows that the Synthetic backup only contains two files because the catalog tables were updated about the deletion of B.txt and hence, during the synthetic backup operation, only files A.txt and C.txt were read from the catalog database for creating a Synthetic single backup set.
The figure below shows the Synthetic Full Backup set contains A.txt and C.txt.
Issue/Introduction
How the Synthetic backup process works with changed data between the Full, Incremental and Synthetic backup stages.
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