ComputingConfidence

First, isntall the isoinfo package.

Use isoinfo -d -i /dev/dvd

Output will look something like:

Logical block size is: 2048
Volume size is: 2172866
Joliet with UCS level 3 found
Rock Ridge signatures version 1 found

The number we are interested in is the volume size.

Next: dd if=/dev/dvd of=/some/path/dvd.iso bs=2048 count=2172866

Notice that the volume size was pasted as my count value.

When dd is done, use growisofs to burn the image

growisofs -Z /dev/dvd=/some/path/dvd.iso

(Note: I think you can also use wodim instead of growisofs)

This procedure will make an exact copy of a data dvd, and is the easiest
if you are trying to replicate bootable discs.

If all you want is to copy the files however, you can alternatively just
do that.  Install the mkisofs package.  (Ubuntu defaults to genisoimage
instead, however, versions prior to hardy have a grievous bug that can
lead to data corruption.)

Then mount your dvd.

mkisofs -r -J -o /some/path/dvd.iso /media/cdrom/.

And when mkisofs is finished: growisofs -Z /dev/dvd=/some/path/dvd.iso