Dell NetWorker 19.9 Administration Guide

How a synthetic full backup is created

When a synthetic full backup operation starts, the NetWorker software performs an incremental backup of the save set and then adds that to the full and incremental backups that are already in place for the synthetic full process. Then the synthetic full backup occurs.

The following figure illustrates how a synthetic full backup is created.

In this example, the synthetic full backup operation creates the incremental backup at T4. Then a synthetic full backup is created by combining the full backup at T1 with the subsequent incremental backups at T2, T3, and T4 to form a synthetic full backup at T4 + Delta. The save set at T4 + Delta is equivalent to a full backup that is taken at T4.

The T4 + Delta represents a small time change of one or two seconds from the time of T4, since two separate save sets cannot be assigned the exact same save set time. For example, if T4 is created at 1334389404, then T4+Delta is created at 1334389405, with a difference of one second.

The synthetic full save set includes only files that are covered by save sets up to T4 at 1334389404. The incremental backup after the synthetic full backup at 1334389405 includes all changes since 1334389404. Note that the synthetic full backup does not include the changes since T4, since only one save set can exist at any particular time.

After a synthetic full backup is performed, the next synthetic full backup combines the previous synthetic full backup and subsequent incremental backups.