Scratches on recordable DVDs ?

[Will Dormann]

I'm not sure if this is appropriate for this group or not. I know
there are DVDR groups, but they mostly seem to be filled with posts like
"Does anybody have a crack for <program>?"


Anyway, I was going to make a "rescue" DVD of a system and I noticed
that the DVD+RW had a scratch on it. I was going to toss the disc, but
then decided to give it a shot just for the hell of it. When I burned
the disc, I had Nero verify the burn after. The disc verified fine!

My question is... how? Is DVD error correction that good? Can a
DVD burner sense where there is a flaw in the recording media? (and
skip over that part?) I burned the disc in a standard "ISO" method, as
opposed to packet/UDF.

My camera doesn't have a macro setting, and I had to play with the color
curve to get the scratch to show up well, but here's a picture of the
scratch:
http://www.cis.ysu.edu/~wdormann/dvdscratch.jpg

With how closely packed the information is on a DVD, I would think that
a scratch like that would be equivalent to, say, a glob of chewing gum
stuck on an LP.

Comments?
-WD

 

[Lil' Dave]

Regularly read alt.video.dvd and dvdr type newsgroups. Of the three
different ones I read, maybe two crack requests total a week. So, I got a
chuckle out of your excuse for not posting there.

If the scratch doesn't touch the substrate nor affect the reflectivity that
the reader "sees", its not really a problem.

The scratch also has to be in the area of the DVD media that's recorded to
affect it. Its obvious to me that its not.
Dave

 

[Will Dormann]

Regularly read alt.video.dvd and dvdr type newsgroups. Of the three
different ones I read, maybe two crack requests total a week. So, I got a
chuckle out of your excuse for not posting there.

Or posts asking about how to copy a DVD. I dunno, to me groups seemed
less technical to me. Maybe I'm wrong.

If the scratch doesn't touch the substrate nor affect the reflectivity that
the reader "sees", its not really a problem.

Since the substrate is sandwiched between two layers of polycarbonate,
it's gotta be one hell of a scratch to touch it! I'm just amazed that
a scratch like that doesn't bend or distort the path of the laser enough
to cause a read error. Or does it?

The scratch also has to be in the area of the DVD media that's recorded to
affect it. Its obvious to me that its not.

Take another look:
http://www.cis.ysu.edu/~wdormann/dvdscratch.jpg

The DVD in question has over 1GB of data on it. And the data is written
from the center of the disc outward. You're saying that the scratch
isn't in the area that is recorded to?

-WD

 

[Arno Wagner]

Lil' Dave wrote:

Or posts asking about how to copy a DVD. I dunno, to me groups seemed
less technical to me. Maybe I'm wrong.

My opinion is that the post is in the correct group. After all it
is a technical question about a storage medium.

Since the substrate is sandwiched between two layers of polycarbonate,
it's gotta be one hell of a scratch to touch it! I'm just amazed that
a scratch like that doesn't bend or distort the path of the laser enough
to cause a read error. Or does it?

It should. With a mostly tangential scratch as this, it should also
cause tracking errors. Error correction is likely not enough. On CD
error correction could span 1 mm tangentially. On DVD it is not much
more, as far as I remember.

Take another look:
http://www.cis.ysu.edu/~wdormann/dvdscratch.jpg

Yes, that would be the typical killer-scratch. Almost tangential and
long. My guess is that DVD is not that dependent on the reflective
layer and that you are still getting a signal good enough for
laser tracking and for error correction to work.

If you want to erxperiment (this disk is now unreliable anyway),
make deeper and deeper scrateches until reading fails.

Arno

 

[SleeperMan]

Or posts asking about how to copy a DVD. I dunno, to me groups
seemed
less technical to me. Maybe I'm wrong.



Since the substrate is sandwiched between two layers of polycarbonate,
it's gotta be one hell of a scratch to touch it! I'm just amazed
that
a scratch like that doesn't bend or distort the path of the laser
enough
to cause a read error. Or does it?

Depends on which side this scratch is. In your case it's in bottom side
(lucky you!). In top side there's only paint to prevent dye and scratch can
very easily damage dye. Try it on one bad CDR or DVD and you'll see.

 

[Will Dormann]

Depends on which side this scratch is. In your case it's in bottom side
(lucky you!). In top side there's only paint to prevent dye and scratch can
very easily damage dye. Try it on one bad CDR or DVD and you'll see.

Your comments are valid for recordable CDs, but with the case of DVD you
are wrong.

With DVDs, the reflective and dye layers are sandwiched between two
layers of polycarbonate.
http://home.clear.net.nz/pages/adbarr/page8.html

This is why when writing on the label side of a DVD with a marker, you
will notice a slight shadow. (as opposed to a CD)


-WD

 

[SleeperMan]

Your comments are valid for recordable CDs, but with the case of DVD
you
are wrong.

With DVDs, the reflective and dye layers are sandwiched between two
layers of polycarbonate.
http://home.clear.net.nz/pages/adbarr/page8.html

This is why when writing on the label side of a DVD with a marker, you
will notice a slight shadow. (as opposed to a CD)


-WD

A-ha- I guess that's one reason some say that DVD's are more reliable...

 

[Arno Wagner]

SleeperMan wrote:

Your comments are valid for recordable CDs, but with the case of DVD you
are wrong.

With DVDs, the reflective and dye layers are sandwiched between two
layers of polycarbonate.
http://home.clear.net.nz/pages/adbarr/page8.html

This is why when writing on the label side of a DVD with a marker, you
will notice a slight shadow. (as opposed to a CD)

Interesting. So the label side is very resilient...

Arno

 

[Scott Alfter]

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Depends on which side this scratch is. In your case it's in bottom side
(lucky you!). In top side there's only paint to prevent dye and scratch can
very easily damage dye. Try it on one bad CDR or DVD and you'll see.

That's only the case with CDs. With DVDs, the recording surface is
sandwiched between two thin discs, not applied to the surface of a thicker
disc. Scratches to the label side of a single-sided DVD-R/RW should have no
effect at all on readability/writability, as long as they aren't deep gouges
that go all the way through the top half of the disc.

_/_ Scott Alfter (address in header doesn't receive mail)
/ v \ send mail to $firstname@$lastname.us
(IIGS( http://alfter.us/ Top-posting!
\_^_/ rm -rf /bin/laden >What's the most annoying thing on Usenet?

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[geno_cyber]

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That's only the case with CDs. With DVDs, the recording surface is
sandwiched between two thin discs, not applied to the surface of a thicker
disc. Scratches to the label side of a single-sided DVD-R/RW should have no
effect at all on readability/writability, as long as they aren't deep gouges
that go all the way through the top half of the disc.

A Verbatim DVD-R 2x disc recently became almost unreadable just by using it on some DVD drives.
I still wonder if it was the HP remarked Samsung drive in a HP desktop PC that broke it. There were
3 big (1cm) scratches on the bottom side which looked deep enough since the colour there changed
completely.
I lost over 800MB of files on that disc, fortunately I had the possibility to copy the other 3GB and
backup them to another disc.
However DVD recordables are less robust to scratches compared to CD-Rs and as soon as you get a very
small serie of scratches the disc becomes unreadable.

 

[J. Clarke]

A Verbatim DVD-R 2x disc recently became almost unreadable just by using
it on some DVD drives. I still wonder if it was the HP remarked Samsung
drive in a HP desktop PC that broke it.

If the drive scratched it that was either a busted drive or abrasive dirt in
the drive and had nothing to do with the brand.

There were 3 big (1cm) scratches
on the bottom side which looked deep enough since the colour there changed
completely.

If they were down to the chemical layer you need to find out what caused
them and fix it--that's something that even a belt-sander takes a while to
do.

I lost over 800MB of files on that disc, fortunately I had the
possibility to copy the other 3GB and
backup them to another disc.
However DVD recordables are less robust to scratches compared to CD-Rs and
as soon as you get a very small serie of scratches the disc becomes
unreadable.

DVDs have a smaller track width, so one should expect them to be more
susceptible to damage. Polish out the scratches and you should be fine.