Switch to DVD backup media from CD?

[Pan]

I'm not convinced with those circles. FAR too regular diameter wise.

Well, I don't have the discs in my possession anymore. But I would agree
that the diameter does look very similar on all the circles given the way
the camera would skew them slightly in the image.

Yeah, thats a real possibility, thats the head hitting the surface.

No, if it is mechanical, it's the *only* possibility I have no idea how
somebody could do that accidentally anyway

That fits the head possibility, its only on one side.

Well, no, it's on most of the disc, but not all of it. There are clear
patches which I don't think fits something actually hitting the disc.
Since it's clear that certain sections have been marked several times and
must of sustained several hits, it seems a little odd to me....

But if the disc didnt get grabbed by the grabber properly...

I'm suppose it's possible. I really have no idea. But given the
information I gave at the start of this particular topic, it seems
unlikely that all of that could of been a coincidence....

I'll print one person's response to this photo when I previously posted
about this problem.

"let me guess - it's the Lethal Weapon collection you're referring to ? Or
at least another fine product from Warner Home Video ;-) ? "

That ain't no coincidence.... since the first guess was spot on.

In addition:

"Warner used some weird materials to produce parts of this DVD set.

A weird solvent has been used in either the bond between the layers of the
DVDs or the printing inks used for the packaging. Over a long period of
time this solvent accumulates on the disc surface in strange patterns. So
don't worry about your DVD drives, they're perfectly fine. "

Not necessarily.

How can it cause marking on a disc like that and be silent?

If you had been at the PC when it happened, anyway.

Actually, both discs were DVD films. So I think I probably was there at
the time.

On the other had its very hard to see how those identical diameter
circles could be produced other than mechanically.

I have to say that this point is quite valid. Let's assume your right for
a moment. No other discs have been affected apart from these two from the
same collection were affected. So what's going on?

This issue brings new meaning to the point about making multiple copies of
things anyway. Look carefully at the photos. That could be your backups

Regards,

Pan

 

[Rod Speed]

Rod Speed wrote

Well, I don't have the discs in my possession anymore. But I would
agree that the diameter does look very similar on all the circles
given the way the camera would skew them slightly in the image.

Yeah, bet they are identical diameter.

No, if it is mechanical, it's the *only* possibility

Not really. Its possible it was a mechanical effect during
manufacture that took some time to become that visible.

I have no idea how somebody could do that accidentally anyway

Guess it might be possible if it was put down
on that round object quite a few times.

Or if you were leaping around on your pogo stick and the CD
happened to be face up on the floor and you didnt notice etc.

Well, no, it's on most of the disc, but not all of it.

I dont think that indicates much.

There are clear patches which I don't think
fits something actually hitting the disc.

The head just didnt hit it there etc.

Since it's clear that certain sections have been marked several times
and must of sustained several hits, it seems a little odd to me....

Sure, but I cant see it can be other than mechanical.

I'm suppose it's possible. I really have no idea. But given
the information I gave at the start of this particular topic,
it seems unlikely that all of that could of been a coincidence....

I'll print one person's response to this photo
when I previously posted about this problem.

"let me guess - it's the Lethal Weapon collection you're referring to ?
Orat least another fine product from Warner Home Video ;-) ? "

That ain't no coincidence.... since the first guess was spot on.

In addition:

"Warner used some weird materials to produce parts of this DVD set.

A weird solvent has been used in either the bond between the layers of
the DVDs or the printing inks used for the packaging. Over a long period
of time this solvent accumulates on the disc surface in strange patterns.
So don't worry about your DVD drives, they're perfectly fine. "

I cant see how any solvent effect can produce such identical diameter circles.

How can it cause marking on a disc like that and be silent?

I didnt mean silent, just not 'extremely noisy'

Actually, both discs were DVD films. So
I think I probably was there at the time.

Dunno, you dont necessarily stay in the room the entire
time that the DVD is in the drive even with a movie.

I have to say that this point is quite valid. Let's assume your right
for a moment. No other discs have been affected apart from these
two from the same collection were affected. So what's going on?

Guess they might have had an off tolerance center hole and
they were the only ones the grabber had a problem with etc.

This issue brings new meaning to the point about making multiple copies of
things anyway. Look carefully at the photos. That could be your backups

Nar, I'd notice those tracks on my backups |-)

 

[Pan]

Not really. Its possible it was a mechanical effect during
manufacture that took some time to become that visible.

True. I thought you were referring to mechanical damage done to the disc
in my care.

Guess it might be possible if it was put down
on that round object quite a few times.

Only if I'd gone totally insane

Or if you were leaping around on your pogo stick and the CD
happened to be face up on the floor and you didnt notice etc.

If I had to be insane for the first to happen, I must of been about to
commit suicide in this case

I dont think that indicates much.


The head just didnt hit it there etc.

But these areas are quite significant in size. Other areas have left marks
as many as fourteen times. Random chance doesn't really account for that.
You could say that it's possible it was hitting only part of the disc. But
that only works from the inside to the outside, not around the disc since
it spins.

I cant see how any solvent effect can produce such identical diameter circles.

Maybe. But how do you explain the person's reaction? After all, he saw the
same picture you did.

I didnt mean silent, just not 'extremely noisy'

I suppose I could potentially of missed that if I was watching a DVD with
headphones on. But I do have an ear for these things, I found out one of
my HD's was dying when I heard the unusual access pattern caused by bad
sectors.

I should also add that the circles were not raised or indented in any way.
It was completely flat.

Dunno, you dont necessarily stay in the room the entire
time that the DVD is in the drive even with a movie.

That's possible I suppose. Since I can't remember if I do or not, I'll
concede the point

Guess they might have had an off tolerance center hole and
they were the only ones the grabber had a problem with etc.

If that's the case, I hope the new copies of the same collection don't
have the same problem......

Nar, I'd notice those tracks on my backups |-)

By the time you noticed that, it's already too late

Regards,

Pan

 

[Rod Speed]

True. I thought you were referring to mechanical damage done to the disc
in my care.


Only if I'd gone totally insane


If I had to be insane for the first to happen, I must of been about to
commit suicide in this case

But these areas are quite significant in size. Other areas have left marks
as many as fourteen times. Random chance doesn't really account for that.

Yes it does with that many total hits.

You could say that it's possible it was hitting only
part of the disc. But that only works from the inside
to the outside, not around the disc since it spins.

Cant see that either if its come off the grabber.

Maybe.

No maybe about it in my opinion.

But how do you explain the person's reaction?
After all, he saw the same picture you did.

Plenty dont understand those basics.

I suppose I could potentially of missed that if
I was watching a DVD with headphones on.

Dunno, I'd expect that to have seriously compromised the DVD audio and video.

But I do have an ear for these things, I found out
one of my HD's was dying when I heard the unusual
access pattern caused by bad sectors.

Sure, but that assumes you were there to hear it when it happened.

I should also add that the circles were not raised
or indented in any way. It was completely flat.

Scratches usually arent that tactile.

That does support it happening at manufacturing time tho.

That's possible I suppose. Since I can't
remember if I do or not, I'll concede the point

If that's the case, I hope the new copies of the
same collection don't have the same problem......

Its likely they would have picked it up and fixed it from the returns.

By the time you noticed that, it's already too late

I still have the original on the hard drives.

 

[Neil Maxwell]

Not to me, FAR too regular for that. Stress fractures arent.

Looks more like something stomped on the DVD, something round.

Stress fractures in a substance with a crystalline structure can be
very regular and repeatable, in both size and shape. Crystal
structure cracks generally will be stopped when reaching other cracks,
as was seen on many of these.

I work with crystal structures quite a bit, and have seen similar
patterns in cracks induced by thermal stresses, generally in a
crystalline substrate that's got flaws of some sort, such as foreign
molecules/atoms that have offset or weakened the crystal structure.

The size of the fractures, as well as their patterns, are often a
factor of the levels of contamination, the size of the contaminants
(atoms, molecules, foreign crystals, dust, whatever) and how evenly
spread they are through the substrate material.

I've never worked with polycarbonate, but it does have an inherent
crystal structure. I'm sure most polycarbonate manufacturing
techniques are geared towards amorphizing it, since crystal structures
in materials reduce toughness (a strong point of amorphous
polycarbonate), but crystal structures are quite persistent.

I would expect something hitting the disk while spinning to leave
circumferential scratches at the impact point, particularly if it's
hitting hard enough to damage polycarbonate in this way. Damage like
this could be made from something pressing on the disk, but I'm at a
loss for a mechanism that would do this in the daily life of a DVD,
particularly just on specific batches.

It would be fairly easy to test for this if some of the original disks
were still available, but that's about the only way to clarify it.
Nonetheless, I've seen quite a lot of complex and unusual stress
fractures in crystalline materials, and that's what popped into my
mind as soon as I saw the picture.

 

[Neil Maxwell]

Do you have any links or times/dates/titles/NGs to such discussions?

A quick Google Groups search on "cdr media failure", "cdr media
failures", "cdr lifetime", "cdr lifetimes", and such (without the
quotes) will bring up quite a lot of material. The posts are starting
to show up for DVDs as well.

If you are interested, 1/2 hour of browsing should prove illuminating.
If you're not, that's fine too - no skin off my back. Many people
don't want to believe that CDRs will fail over a few year period, for
whatever reason. I've learned about it through personal experience
and have researched it extensively, and whether anyone else believes
doesn't matter to me.

The earliest web discussions I found was on a Mac board, back in 2000:

http://www.macintouch.com/cdrfailure.html

These folks use non-data-driven 'net consensus to decide that using
good burners and good media will avoid the problem. They also come up
with many recommendations that are now known to be bogus; again, it's
the tribal knowledge effect of people parroting what they've seen/been
told without having actually seen or performed any real-world testing.

CDR lifetime data is mostly marketing-driven. Read the lifetime
claims, and look for the source data they use to make them.

Your the first I've seen make such a claim.

Heh! I believe you haven't been paying attention to this particular
issue. I have, for some years now, and there's been quite a bit of
discussion on it, both on usenet and on the web, as pointed out above.
It started popping up with regularity back in '98-99.

The expert consensus is summarized(they last a damn long time but how long
is unclear yet) here:
http://www.itl.nist.gov/div895/carefordisc/CDandDVDCareandHandlingGuide.pdf

You and I have different definitions of expert consensus, though
you're right about one thing - the results are unclear. They admit
the data is incomplete, and state that "much more needs to be done".
Their conclusions on dye layer lifetimes are carefully worded to show
that they have nothing but manufacturer's data for this, and they use
lots of words like "should", "not always clear", "expectations vary".
It's not what you call scientifically rigorous.

As far as I can see, this report is a collection of tribal knowledge
and 'net wisdom, with very little hard source data to build it on.
Much of it is true, of course; it's simple to test whether sunlight
and UV is damaging to CDRs, the effects of flexing and scratching
disks, and such, but for lifetime estimates, there's just no good
data.

I assume you didn't follow the links in their bibliography. I did,
when this report was last updated (it's very tedious), and there is
extremely little actual hard scientific data from non-biased,
peer-reviewed studies in these sources. Maybe I missed an actual
study of real-life dye layer degradation resulting in data loss, but I
don't think so.

The fact is, nobody's publishing any studies on CDR and DVDR aging
(and I'm sure the companies are performing these studies), except for
accelerated lifetime testing, which is far too immature in this arena
for good data. Consumer CDR burning has reached the 10 year mark this
year, based on the release of the HP 4020i for under $1000 in 1995ish.
To claim 20 or 50 or 100 year lifetimes on 10 year old technology
that's still undergoing dramatic changes in both burners and media is
just plain silly, IMO, and is completely unsupportable.

That would include me.

That's good for you. Only 7 years to go to reach your 15 year mark.
Best of luck to you.

 

[Rod Speed]

Stress fractures in a substance with a crystalline structure

It isnt a crystalline structure, its a polymer.

can be very regular and repeatable, in both size and shape.

But are never identically just one size circles, with some
of those circles with part of the circumference missing
and never a nested set of circles seen in this case.
http://www.colinjones.co.uk/images/dvd-damage.jpg

Crystal structure

A DVD aint a crystal structure, its a polymer.

cracks generally will be stopped when reaching
other cracks, as was seen on many of these.

Nope, and you dont get JUST perfectly circular 'cracks'
even with crystal structures either. In spades with the
nest set of circles seen in the middle right of jpg.

I work with crystal structures quite a bit,

A DVD aint a crystal structure, its a polymer.

and have seen similar patterns in cracks induced by thermal stresses,

Dont believe it, in spades with the nest set of identical
diameter circles seen in the middle right of jpg.

generally in a crystalline substrate that's got flaws of some sort, such as
foreign molecules/atoms that have offset or weakened the crystal structure.

A DVD aint a crystalline substrate, its a polymer.

The size of the fractures, as well as their patterns, are often a
factor of the levels of contamination, the size of the contaminants
(atoms, molecules, foreign crystals, dust, whatever) and how
evenly spread they are through the substrate material.

I've never worked with polycarbonate, but
it does have an inherent crystal structure.

Like hell it does, its a polymer.

I'm sure most polycarbonate manufacturing techniques
are geared towards amorphizing it, since crystal structures
in materials reduce toughness (a strong point of amorphous
polycarbonate), but crystal structures are quite persistent.

A DVD aint a crystalline substrate, its a polymer.

I would expect something hitting the disk while spinning to leave
circumferential scratches at the impact point, particularly if it's
hitting hard enough to damage polycarbonate in this way.

But its not necessarily spinning, particularly if its come off the grabber.

Damage like this could be made from something pressing on
the disk, but I'm at a loss for a mechanism that would do this
in the daily life of a DVD, particularly just on specific batches.

It could have happened during manufacture, and the diam
of the marks is surprisingly close to the diam of the hole.

Bet it was done by the grabber.

It would be fairly easy to test for this if some of the original disks
were still available, but that's about the only way to clarify it.

Sure, but we still have the fact that the pattern is identical
sized circles, usualy with some of the circumference
missing, and sometimes nested. Thats not stress fractures.

Nonetheless, I've seen quite a lot of complex
and unusual stress fractures in crystalline materials,

A DVD aint a crystal structure, its a polymer.

and that's what popped into my
mind as soon as I saw the picture.

Bet you've never seen such identical sized circles,
usually with some of the circumference missing,
and sometimes nested, with any stress fracture.

 

[Ron Reaugh]

Right, there is no evidence that well stored CDRs go bad over modest time.
The issue is whether they last 15, 50 or 150 years as I said. More data is
needed but from where I'm sitting the answer sseems to be that just like the
Energizer Bunny well stored CDRs just keep going and going.

 

[Yoshi]

Do we have to discuss wheter they last more than 50 years ?
If disks themselves last, the drive will be gone in such long years, I
think.
As same as FD, in 50 years, we probably find the PC that has no FD
drive.

 

[J. Clarke]

Do we have to discuss wheter they last more than 50 years ?
If disks themselves last, the drive will be gone in such long years, I
think.
As same as FD, in 50 years, we probably find the PC that has no FD
drive.

We find that now. But there are so many diskette drives out there that that
should not be a problem. And there are more CD drives out there than FD.

 

[Neil Maxwell]

Like hell it does, its a polymer.

A google on polycarbonate crystal structure will bring up quite a few
links, mostly research papers and theses, that refer to it.

A few selections:

http://www.eng.uc.edu/~gbeaucag/Classes/Morphology/Chapter2html/Chapter2.html
Materials such as Polycarbonate are usually used in the glassy state
even though they can crystallize under the proper conditions. Usually,
better mechanical properties result from lower degrees of
crystallinity in polymers.

http://digitalcommons.uconn.edu/dissertations/AAI3080933/
The effects of zinc sulfonated polystyrene ionomer (ZnSPS) on the melt
crystallization of bisphenol A polycarbonate (PC) were investigated.
Melt crystallization of pure PC is extremely slow due to its rigid
chain.

http://scholar.lib.vt.edu/theses/available/etd-12072001-143139/unrestricted/RSF1Thesis.pdf
A Study of Crystallization in Bisphenol A Polycarbonate
The crystallization behavior of bisphenol-A polycarbonate (BAPC) was
studied, focusing on the initial stage of crystallization and the
secondary stage of crystallization.
....
Since polycarbonate has only one crystal structure, the crystallinity
and structure can be frozen and thoroughly studied.

 

[Neil Maxwell]

Do we have to discuss wheter they last more than 50 years ?
If disks themselves last, the drive will be gone in such long years, I
think.
As same as FD, in 50 years, we probably find the PC that has no FD
drive.

IMO, the issue is not so much whether they'll last 50 years (I don't
know of any digital medium that this can reliably be claimed for,
short of punch cards - platinum ones are best), but whether they can
reasonably be expected to last 2-5 years or more.

Again, folks are free to do whatever they like with their data. I've
made my decisions, but I tend to be somewhat cautious.

 

[Neil Maxwell]

Right, there is no evidence that well stored CDRs go bad over modest time.

It takes much less data to show something may fail than to show that
it won't. I have data that I trust, and it's all I need, particularly
as it's supported by other people's data (though I trust the other
data less). You're free to gather your own data (or not).

The issue is whether they last 15, 50 or 150 years as I said. More data is
needed but from where I'm sitting the answer sseems to be that just like the
Energizer Bunny well stored CDRs just keep going and going.

Yes, I have an IBM 75GXP drive that is still working very well. From
where I'm sitting, there are no issues with them - mine's like the
Energizer Bunny. I still don't use it for any data I can't afford to
lose, as I don't trust them.

YMMV, as always.

 

[Ron Reaugh]

Do we have to discuss wheter they last more than 50 years ?
If disks themselves last, the drive will be gone in such long years, I
think.

Right but if they DO reliably last that long then capabilities to read them
will continue to be around.

As same as FD, in 50 years, we probably find the PC that has no FD
drive.

Floppies DO go bad merely with time so the requirement for a floppy drive in
say 50 years seems much lower.

 

[chrisv]

Right but if they DO reliably last that long then capabilities to read them
will continue to be around.


Floppies DO go bad merely with time so the requirement for a floppy drive in
say 50 years seems much lower.

Pick a name and stick with it, Rod.

 

[Rod Speed]

A google on polycarbonate crystal structure will bring up quite
a few links, mostly research papers and theses, that refer to it.

All of these are completely useless on what is being discussed,
whether those constant diameter circles, some of them nested,
have anything to do with any purported crystal structures. They dont.

A few selections:

http://www.eng.uc.edu/~gbeaucag/Classes/Morphology/Chapter2html/Chapter2.html
Materials such as Polycarbonate are usually used in the glassy state even
though they can crystallize under the proper conditions. Usually, better
mechanical properties result from lower degrees of crystallinity in polymers.

Says nothing useful what so ever about whether the
polycarbonate layer in a DVD is a crystal structure. It aint.

http://digitalcommons.uconn.edu/dissertations/AAI3080933/
The effects of zinc sulfonated polystyrene ionomer (ZnSPS) on the melt
crystallization of bisphenol A polycarbonate (PC) were investigated.
Melt crystallization of pure PC is extremely slow due to its rigid chain.

Says nothing useful what so ever about whether the
polycarbonate layer in a DVD is a crystal structure. It aint.

http://scholar.lib.vt.edu/theses/available/etd-12072001-143139/unrestricted/RSF1Thesis.pdf
A Study of Crystallization in Bisphenol A Polycarbonate
The crystallization behavior of bisphenol-A polycarbonate
(BAPC) was studied, focusing on the initial stage of
crystallization and the secondary stage of crystallization.
...
Since polycarbonate has only one crystal structure, the
crystallinity and structure can be frozen and thoroughly studied.

Says nothing useful what so ever about whether the
polycarbonate layer in a DVD is a crystal structure. It aint.

 

[Rod Speed]

Do we have to discuss wheter they last more than 50 years ?
If disks themselves last, the drive will be gone in such long years, I think.

Not necessarily something that will read the disk tho.

As same as FD, in 50 years, we probably
find the PC that has no FD drive.

A better example is the LP record and slides. While the original
may not be seen that much anymore, thats a separate issue to
whether the media can still be read when that is required.

Punched cards and paper tape can still be read even now.

 

[Pan]

Again, folks are free to do whatever they like with their data. I've
made my decisions, but I tend to be somewhat cautious.

I think Neil is quite right in this assessment. I think it's not really
important who has the most accurate prediction on how long CD/DVD discs
will last. But since nobody could argue that single discs *could*
potentially fail in time, those who have important data will need to
protect it anyway with safeguards

Regards,

Pan

 

[Pan]

Plenty dont understand those basics.

That's not what I meant. The person immediately narrowed down
the DVD to the correct set, in fact, his first guess was spot
on. He later implied that he'd seen it himself, although I'll
confess he didn't come out and say it. But how else would he of been able
to identify the disc so accurately?

Dunno, I'd expect that to have seriously compromised the DVD audio and video.

That's true. I could of happened potentially when I wasn't about and the
disc was in the drive, but I normally keep the discs in their cases. That
sounds extremely unlikely to me.

Scratches usually arent that tactile.

I know, I just thought I should mention it. It wasn't tactile at all, the
surface was completely smooth.

That does support it happening at manufacturing time tho.

I'll confess that when I saw it, I expected to feel pieces of the surface
had been scratched out by the visual look of what had happened. But
it was totally flat.

Its likely they would have picked it up and fixed it from the returns.

I agree and sincerely hope that is the case.

I still have the original on the hard drives.

Oh right. So you keep all your backups on HD as well as DVD? I assume you
use large hard disks?

Regards,

Pan

 

[Rod Speed]

Rod Speed wrote

That's not what I meant. The person immediately narrowed
down the DVD to the correct set, in fact, his first guess was
spot on. He later implied that he'd seen it himself, although
I'll confess he didn't come out and say it. But how else
would he of been able to identify the disc so accurately?

OK, understand what you meant now.

That's true. I could of happened potentially when I wasn't
about and the disc was in the drive, but I normally keep the
discs in their cases. That sounds extremely unlikely to me.

Unless you were temporarily out of the room for a piss etc.

I know, I just thought I should mention it. It wasn't
tactile at all, the surface was completely smooth.

Yeah, that does support the manufacturing time possibility.

I'll confess that when I saw it, I expected to feel pieces
of the surface had been scratched out by the visual look
of what had happened. But it was totally flat.

Yeah, that does support the manufacturing time possibility.

I agree and sincerely hope that is the case.

Oh right. So you keep all your backups on HD as well as DVD?

Yep, basically because I dont do photos or home video.

I assume you use large hard disks?

Currently the biggest is 160G, just because I am waiting for samsung
to get off their fat arses and produces their 250G drives. Currently only
the 200G drives are buyable in my country yet and thats only been for
about a month now. I've changing over to a PVR done on a PC with
3 digital TV tuner cards, so things are getting a bit tight at the moment.

I dont bother to back that sort of thing up to DVD, just have
some stuff on DVD due to a shortage of hard drive space.

Digital TV is a fair consumer of hard drive space, 2-3G per hour
depending on the channel and lots of computing horsepower and
time needed to crunch that back to 350M or 700M per hour avis
so I dont bother. I keep almost nothing once I have watched it.