Reliability of recording media

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Offline Atomic-S

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Reliability of recording media
« on: 24/06/2007 07:12:46 »
Having had some trouble with my computer's CD-RW | DVD combo rewriter, I have observed the phenomenon of 2 closely similar disks, CD-RWs, both supposedly containing good data files, one turned up unreadable, the other was mostly readable but had a few bad files.

Question: Does data once written onto these disks stay there, or does it slowly evaporate?  I am loathe to rely upon these disks for backup, only to find when I need them that they have self-erased. Has anyone any knowledge or experience in this area, and are some types of disks better than others?



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Reliability of recording media
« Reply #1 on: 24/06/2007 11:24:04 »
You need to eliminate your combo rewriter from the equation by trying to
1. Read more disks from another machine.
2. Read disks you have burned on your machine, using someone else's.
3. Take your 'duff' discs and look on another machine; check they really are duff.
4. Try a different batch of discs.
5. Verify any copies you have made.
6. Record slower than maximum speed- there's always an option for this; if your computer is elderly and slow, your other tasks may be too taxing for it.

Whilst you can't 'rely' on these discs for  rock-solid  backup (banks wouldn't use them, for instance), they are usually pretty reliable.   Certainly, for important data you can make sure of a reliable backup by backing up twice - even duplicate files on the same disc.
They can be damaged by a lot of heat or sunlight, I believe, but they are amazingly robust, all things considered. I have had much less trouble with this medium than with the good old floppys.
I have a feeling that steps 1,2,3 or 4 will indicate that you should  buy a new drive or take it back to the shop. Try it.



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Reliability of recording media
« Reply #2 on: 25/06/2007 02:17:48 »
Certainly, my experience is that CD-RW is far more reliable than floppies, I have had problems with CD-RW's written on early generation machines being read by later generations of CD-RW readers (and DVD readers reading CD's will have their own variables to contend with).

The CD specifications have considerable error correction built in, so that it should be able to sustain significant amounts of local damage to the CD without compromising the overall integrity of the data; but there is no doubt that no recoding media is 100% reliable (even worse, if one is looking for long term storage of data, you may well find that media you right today may simply not have any device capable of reading them in 10 or 20 years time - try finding something that can still read 8 inch floppies from 30 years ago).

Generally, I have found that that CD-RW's (and CD's written on combo drives), once successfully written (and I do find that the original writing process can sometimes be less than reliable, and so you should always verify the written data) is generally fairly stable, but the greater risk is that over time, the specifications of the devices will subtly change, so that it cannot always be read on future generations of CD readers.


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Reliability of recording media
« Reply #3 on: 27/06/2007 16:44:21 »
As has been previously mentioned, always make a second copy of those crucial files even on the same disc. choose a lower writing speed and always verify the data.

For documents i prefer to use flash drives instead of discs.