When are synthetic backups created?

SUMMARY

Describes when synthetic backups are created by the Unitrends appliance.

ISSUE

This article describes when synthetic backups are run by the Unitrends system.

Backup Strategy
The Unitrends product allows users to create flexible backup schedules to meet their recovery time and recovery point objectives. For customers having a small recovery point objective, typically measured in hours, the incremental forever strategy works well. This strategy requires that protected data be sent over the local area network to the backup system only once. After the initial master or full backup is performed over the network, all subsequent backups only capture the incremental changes from the previous successful backup.  This optimizes network resources on the LAN, as well as significantly shrinking the backup window that can be incurred while backing up big data sets.  In order to facilitate this backup strategy, incremental backups are periodically “synthesized” or coalesced into a full backup as explained below.

Synthetic backups
Synthetic backups are created by taking a base full backup and superimposing the incremental backups on the full. Upon superimposing the incremental backups, a new recovery point is available which has the previous full and all subsequent changes rolled up into a new full backup. This backup is the synthetic full backup.  The point at which the system synthesizes backups into a new full is determined by a number of factors. Some of the factors are:

-Amount of data being protected on the backup system
-Number of days from the last synthesized full
-Number of incremental backups in the current chain
-Load on the system

For a backup system that is not archiving or replicating, a synthetic full should occur once in two weeks. For a system that is archiving or replicating, in addition to the synthetic full backup, a daily synthetic differential backup is also created for file-level backups.  The synthetic file-level differential creates an extra recovery point that can also be leveraged for daily replication and archiving.  Synthetic backups are created for file-level backups, VMware and Hyper-V application backups.
 
Synthetic backups are compressed and optionally encrypted inline.  Synthetic backups are either deduplicated inline (appliances deployed with version 8.2 or later) or post processed deduplicated (older appliance deployments). Synthetic backups display in the user interface as regular full/master or differential backups. When viewing backup details, type is synthetic.

See Synthetic backups in the Recovery-Series and UEB Administrator's Guide for additional infromation.

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