DVD9 is an 8.5gb DVD format. The data is stored on a single side of a disk, but in two different layers. To burn this format, you need a “double layer” or “dual layer” burner, and a blank “DL” disk, which are more expensive than regular DVDs. Double-layer burners are cheap and common, however if your burner is several years old, you will probably need to upgrade.
You may also need to upgrade your burning software. The software that came with older burners probably won’t work. You can also use ImgBurn (donation-ware).