Synthetic full backups consolidate the data from the latest full backup or synthetic full backup together with any subsequent incremental backups, instead of reading and backing up data directly from the client computer. Since synthetic full backups do not back up data from the client computer, this operation imposes no load on the client computer.
During a synthetic full backup, a list of objects from previous backups is generated, and the latest version of each object is considered, in order to build a new backup image.
Advantages of Synthetic Full Backups Over Full Backups
Synthetic full backups have the following advantages over full backups:
- They impose a lighter load on the production environment because they are created by consolidated data from the backup repository, rather than from the client computer.
Note
Using synthetic full backups can cause unintentional expiration of data since retention periods are defined by the number of full backup cycles. For example, running a synthetic full immediately after a standard full backup does not consolidate any data (as the standard full already includes all the backup data); storage resources might be unnecessarily consumed.
Automatic Synthetic Full Backup Schedules
The automatic synthetic full backup schedule will trigger a synthetic full backup job if any of the following conditions are met:
-
Run Synthetic Full - Every X days. Defines the number of days that should pass between automatic synthetic full backups.
-
Run Synthetic Full - As needed for extended retention. Defines the number of days that should pass between synthetic full backup jobs based on the storage policy’s extended retention rules defined by the user. If extended retention rules are not configured, then the system ensures that a synthetic full backup job is run at least once every 30 days.
Note that, even if extended retention rules are configured and set to retain full backups that are less than 7 days (for example, Hourly Full backups or Daily Full backups), the synthetic full backup jobs will not run more frequently than once every 7 days.
A storage policy’s extended retention rules will apply the setting with the least number of days. For example, if Extended Retention Rules for Full Backups is set to 15 days, and Automatic Select Full Backups is set to 20 days, the system will apply only the Basic Retention Rules for All Backups (15 days).
Run Synthetic Full - As needed to reclaim space. Automatically triggers a synthetic full backup job to reclaim space from backed up media. The criteria for this option to run the schedule is if there is a large amount of space to be reclaimed.
For file systems and VMs, automatic synthetic full backup job will be triggered by this option if at least one of the following conditions is met:
-
The current application size is greater than or equal to 1 GB.
-
The sum of the sizes of the backup jobs in the current cycle is greater than or equal to 1 GB.
-
The sum of the sizes of the backup jobs in the current cycle is greater than the current application size by more than 50%.
A full backup job and subsequent incremental backup jobs or differential backup jobs must exist before a synthetic full backup job can run.
The system will not run a synthetic full backup job if no incremental or differential backups were run after the last full or synthetic full backup.
The system will not run a synthetic full backup job if a full or synthetic full backup job has run in the past 7 days.
If an automatic synthetic full backup job fails, the next attempt happens after 24 hours.
If a manual synthetic full backup job is run for subclients associated with an automatic schedule, the schedule is skipped and the next job runs based on when the criteria is met next.
An automatic synthetic full backup schedule can’t be configured to run on a specific day/time of the week/month/year, as the schedule is triggered instead based on the three criteria mentioned above. Therefore, if there is a need to run a synthetic full backup on a specific day/time of the week/month/year (for example, on the last day of every month), then you should run a fixed time synthetic full backup schedule (that is, Daily, Weekly, Monthly, or Yearly).