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Will recorded data CD's / DVD's deteriorate faster if stacked vs kept in separate cases?

Posted on 2007-07-20
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I've got dozens of "old" backup CD's and DVD's.   The "latest", "good" ones are kept separately (including double copies, encrypted, off-site).  Due to probably irrational thinking, I'm reluctant to trash the old backups (postponing that day, which will surely come...)

My question is, all other factors being equal, will they deteriorate any faster if I just stack them together without cases, for instance on a spindle, instead of keeping them in separate cases?  (I've already got some doubled up in cases).  

Any opinions on this would be appreciated.

Thanks!
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Question by:codequest
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by:r-k
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ID: 19533188
I don't have any hard data to back this up, but definitely anything that allows some air circulation or relieves pressure on the disks should be a good thing. Putting them in paper sleeves should be almost as good, however, and save space. Just be sure they are stored on edge and not flat for long-term storage. Things to avoid are heat, humidity, bright light etc.
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by:SysExpert
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I agree that storing them standing up is much better than lying flat, so that should be your main concern.

I hope this helps !
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by:kode99
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Lying flat, standing up etc. is irrelevant.  Stacked or singles is probably also irrelevant but if I had to guess stacked disks on a spidle are probably more protected than single disks - much less surface is exposed.

Disks decay is a chemical process,  which is why temperature and light are things to avoid.  Light and heat speed chemical processes.  

Also pressue is irrelevant,  the accumlated weight of a large stack of disks is not enough to deform or otherwise have an effect on a single disk or the decay process.  The plastic is quite durable,  probably outlive the data.

I highly doubt that every disk manufacturer would make, warehouse and distribute disks in spindles designed to stack disks flat on each other if this was in fact bad for the disks.

Just keeping them in proper environmental conditions,  dark, dry and room temperture.

One thing to be careful about though is disk cases that the disks snap into too tightly.  These can cause stress cracks starting from the hole in the middle of the disk.  
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by:codequest
ID: 19536247
Thanks for the inputs.  While the views are mixed, I think that I'm getting that for my "should toss 'em anyway" copies I can't go too wrong if I keep them cool and in the dark.

This does prompt me to keep the "good" backups refreshed regularly, though...
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by:codequest
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BTW, not much use to sort the answers on credentials  :-)
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by:r-k
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"does prompt me to keep the "good" backups refreshed regularly"

Yes, highly recommended. I'd say read them back every year or two and maybe copy to new media every 5 to 10 years.

I recently has a chance to read back some CD's written 8 years ago and I was happy to note that all read back without error. The same cannot be said of some floppies from 15 years which show numerous read errors.

kode99: You have some valid points, but I am not sure about the assertion that lying flat vs. on-edge is irrelevant. We are talking long-term here, say 10 to 20 years, so what is a seemingly small pressure now can really add up over the long term. Pending some scientific study of this I'd rather err on the side of caution. The disk manufacturer's have a completely different agenda - they rarely expect the blank disk spindles to sit on the shelf more than a few months and long term storage is not what they designed those spindles for. However, I too am going on instinct mostly, so could be wrong as well.
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by:r-k
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BTW, someone recommended CDCheck recently as a way of checking CD data integrity without haveing to read each file back. Haven't used it, but in case you consider it useful the link is: http://www.kvipu.com/CDCheck/
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by:codequest
ID: 19536358
Cool, good info on the CDCheck.  Though I'm hoping that within 10-20 years  years the problem will be finding a CD reader....
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kode99 earned 800 total points
ID: 19536600
If you actually measure or calculate the pressue placed on CD's in a big stack you would find the the actual pressure is so small compared to the amount of pressure that would be required to deform the plastic, or even stress it, this makes it irrelevant.  Even over time the failure due to decay of the recording surface is going to occur long before the plastic fails.

The pressure is only spread out over the center ring portion of a disk.  If you look at a spindle of disks you will find that the center ring is the only portion of the disk in contact. Even over this reduced area it would take a incredible amount of compression force to deform a disk.  These things are designed to withstand some pretty high forces,  they spin up to several thousand RPM's with a effective zero failure rate for years.

Sony calls their disks sold on spindles 'Storage Spindles' and are fairly durable stackable plastic containers.  Pretty sure the intent is for storage.

If you want to verify disks just use any MD5 utiliy on the original data.  Periodically check the md5,  if the result changes you know the data has changed.  No need to even buy a utility to do this, tons of free ones available.  It has the advantage of being simple and you can write the md5 result right on the disk for easy reference.

Two of the biggest problems with backups are,  
1. people don't do them
2. people don't check them

Also DO NOT use CD-RW media for long term storage. It just does not last.

You are right though,  its all i the environment.  Historically same deal with most storage media - even books.  Problem is usually that stuff gets stored in basements where the humidity factor kicks in.

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by:r-k
ID: 19631372
Thanks and good luck.
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