In 15:
Backup will be saved to the path you given if the backup is successful and the backup will be saved to “/var/spool/asterisk/backup/backup_name/” folder if the backup fails.
For example if you are using you are setting your local backup path as “/home/backup” then your backup will be saved in “/home/backup” if your backup is successful without any errors.
And if your backup fails for some reason then the backup will be saved in “/var/spool/asterisk/backup/your_backup_name/”.
And to possible reduce @bcollins confusion, "__ASTSPOOLDIR__" translates to /var/spool/asterisk by default. And traditionally the backups where written to /var/spool/asterisk/backups/