The Directory Server provides support for incremental backups, which only backs up items that have changed since the last full or incremental backup on the system or since an earlier specified backup.
You must place incremental backups in the same backup directory as the full backup on which they are based.
Note:
Not all backends support incremental backups. If a backend does not support incremental backups, the --incremental option has no effect, and a full backup occurs.