在 DVD+RW resource site:

http://www.dvdplusrw.org/faq/dvdplusrwfaq03.html

有大概提到這個問題...

Can I copy the contents of a DVD-Video disc using a PC DVD+RW drive?

Using a PC DVD+RW drive and the appropriate DVD-Video premastering software, you are able to create full DVD-Video compatible discs on your PC. Using the proper tools it is even possible to make a 1-on-1 copy of a DVD-Video discs, including its navigation and menus, provided that it is not CSS-protected.

Note however that most pre-recorded DVD-Video discs use both layers (and as such are using up to 9 GB of storage space), and that DVD+RW only supports one layer (4.7 GB). Therefore, it will never be possible to make a 1-on-1 copy of a dual layer DVD-Video disc. The same goes for the other recordable DVD-formats like DVD-R, DVD-RW ("minus" RW) and DVD-RAM.

它說 "DVD+RW only supports one layer"
也提到不只是 DVD+RW,
現階段 dual layer 要做 1-1 對拷在 DVD-R/RW 與 DVD-RAM 上,
仍屬不可能的任務.

不管是 DVD+ 陣營還是 DVD- 陣營,
未來也許真的會有 dual layer 的空片跟燒錄機,
但可能還需要一段時間...