kernel 2.6.7, PIONEER DVR-106D (firmware= 1.08) and * DVD±RW format utility by <appro@fy.chalmers.se>, version 4.8. I have 2 problems:
No, you don't:-) All you have to do is to call things by their true name.
1) I can't overwrite on a dvd+rw:
As far as I can see you never tried to overwrite a DVD+RW. You tried DVD-RW! If you want DVD-RW to act more like DVD+RW, i.e. to have an option to just overwrite over previous recording without any explicit preparation, then you have to format it for Restricted Overwrite with dvd+rw-format -force.
2) After a blank (dvd+rw-format -blank /dev/scd1), the media seem to be exactely in the same state than when i have neve use it
No, it's not. After minimal blank procedure media can be used only for DAO recording [or re-formatting for Restricted Overwrite]. So that "engaging DAO" is perfectly expected.
I can write data on, but growisofs -Z says that: " /dev/scd1: FEATURE 21h is not on, engaging DAO... "
All this is discussed on http://fy.chalmers.se/~appro/linux/DVD+RW/-RW/ page, "which mode is one for me." A.