I am writing software to burn CDs and DVDs. (See http://bwgburn.sourceforge.net for more details.) From what I understand with DVD+RW media, you do not do a complete format, but rather begin the format process and it completes in the background. There is a foreground part that runs to completion before the FormatUnit request returns, then the format continues in the background. If you request a write into the area where the disk has not been formatted, the drive will delay until that area of the disk is formatted. If you write from the beginning of the drive, then as long as the format stays ahead of you, the format time is completely hidden.
I have coded my DVD burner software based on this assumption, but when I issue the FormatUnit request, it runs for what I see as a long time (> 10 minutes) and never returns.
So my question is, how long does it typically take to have for FormatUnit command return with the format running n the background.