Full Backup Automatically Converts to an Incremental Backup
Article ID: DLO0001 Full backups automatically convert to incremental backups even when you explicitly select the Full backup option.
If you selected the Full backup option (Advanced Backup Options dialog box), when you run a backup job, an incremental backup runs instead followed by a synthetic full backup.
In the Subclient Properties dialog box (Retention tab), if the number of days you specify in the Use storage policy copy retention after n days box is 1 or higher, then any full backup is converted to an incremental backup followed by a synthetic full backup.
The Full backup is converted to an incremental backup, then followed by a synthetic full backup, to honor the number of days specified in the Use storage policy copy retention after n days box and to carry forward the deleted items for the specified number of days within the current backup cycle.
However, the first backup job runs as a Full backup.