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Jorge Peixoto de Morais Neto schrieb: |
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> On Wed, Nov 26, 2008 at 12:26 PM, Florian Philipp |
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> <lists@f_philipp.fastmail.net> wrote: |
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>>> As for my photos, I can back all the collection to a single DVD (and |
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>>> to a second one, since I keep hearing that DVD-Rs are unreliable), and |
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>>> since I don't take new photos every week, this solution is fine. |
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>>> |
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>> A second DVD-R won't solve the problem because optical disks degrade over |
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>> time and the second one will degrade just as fast as the first. What you |
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>> need to do is to check the disks periodically (once a year is a good time |
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>> frame). |
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> I know DVD-Rs degrade, but it is unlikely they would fail at the same |
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> time, so copying twice does significantly alleviate the problem |
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> (AFAIK) |
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I'm not so sure in this regard. If we were talking about HDDs you were |
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right: it is very unlikely for two of them to fail at the same time due |
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to mechanical defects. But we are talking about optical media. They fail |
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because of chemical reactions. That's why two disks, stored equally, |
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bought at the same time from the same trader, produced by the same |
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company, should degrade equally fast and therefore fail at about the |
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same time. And since you want to check them less than once a year, "at |
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about the same time" means within the same year. |
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> Once a year isn't overkill? Isn't once every two years fine? |
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> |
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I'm not sure. I myself wouldn't trust normal CD/DVD-Rs for more than |
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three years and CD/DVD-RWs for more than one year (cheap RWs degrade |
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much faster than Rs). |
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Additionally, having such long intervals between checks makes it easier |
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to forget them completely. Can you remember whether you checked your |
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disks last year or the year before? I know I couldn't. |
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> Sure. I am doing that since some time now. Unfortunately I didn't do |
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> so for some old backups. But data DVD-Rs have a considerable amount of |
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> correction code, and if the copy from DVD to hard disk proceeds |
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> without a single error message, there is a quite good chance that the |
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> files are good, right? |
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I would think so. |
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