What are Synthetic Backups?

A synthetic backup is identical to a regular full backup in terms of data, but it is created when data is collected from a previous, older full backup and assembled with subsequent incremental backups. The incremental backup will consist only of changed information.

Let’s take an example to understand:

Full Backup	1st December	1024 MB
Incremental Backup	5th December	200 MB
Incremental Backup	9th December	300 MB

A synthetic backup is needed if the backed up file needs copying as a single backup entity, or if it needs restoring. The contents of a synthetic backup differ depending upon the date chosen.

In our example two synthetic backups could be produced: one for 5^th December; and one for 9^th December. The data they contain would be different; the 5^th December synthetic backup would not contain any changes to the file subsequent to that, whereas the 9^th December synthetic backup would.

Information to know regarding Synthetic Backup

1.     It helps reduce the resources needed to backup. A full backup will require a set of server cpu cycles, some network bandwidth and backup media space. Each time you do a full backup you would need the same level of these three resources. By running an incremental backup you need only a fraction of the server CPU cycles, network bandwidth and additional backup media space. That reduces the backup window, the time needed to run the backup, considerably

2.     Incremental Backups increases the time needed for a restore because now a restore would need to return to the user the original backup file and all subsequent incremental backup files, and then the restored file needs re-building to merge in each incremental backup file's data. It takes more time, uses more server cycles and network bandwidth.

3.     By consolidating the original backup file and incremental backup files into a single Synthetic Backup the restore speed is faster because just one file now needs streaming to the user. Also the server CPU cycles needed for the restore are cut back.

4.     Synthetic full backups are media-based; they read backup data from one media and simultaneously write (restore) the result to the new active media within the same media group. As a result, synthetic full backups require that at least two media drives for the same storage policy be available at the time the job is started.

5. Synthetic full backups consolidate data; they do not back up data from the client computer. You should therefore use synthetic full backups in addition to and not in place of any regularly scheduled incremental or differential backup jobs.