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Author Topic: CD Bitrot & repair  (Read 2082 times)

sevenlayermuddle

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CD Bitrot & repair
« on: April 22, 2014, 06:08:49 PM »

Bit of a happy adventure today. :)

A friend popped by last night to ask me if I could help them view some photos on a CD they'd been given. 

Try as I may I could not see any physical damage to the original disk, but XP wouldn't load it at all, nor would OS/X.   Linux let me mount it, it contained a half dozen very large .jpgs dated 2002.  But each of the photos got a read error when viewed, displaying just the first few lines of pixels of each photo, then nothing.

So, for the first time, I had an opportunity to try 'ddrescue', http://www.gnu.org/software/ddrescue

ddrescue ran for probably about two or three hours, going through its various phases, after which I mounted the rescue image….  And was pleasantly surprised to find two nearly perfect photos.  The remainder, whilst still marred by a few blank pixels here and there (usually in lines), rendered fully once again all the original content clearly visible.  Thus I was able to burn a new CD and return to grateful owner.   A huge success then, though I say it myself.  :graduate:

Shame about the bitrot though, first time I've come across it. :o
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burakkucat

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Re: CD Bitrot & repair
« Reply #1 on: April 22, 2014, 06:17:00 PM »

Very interesting.  :)

Just one quick query, please. What did you use as the input to ddrescue? The individual JPEG files? The raw CD image? Or . . ?  :-\
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sevenlayermuddle

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Re: CD Bitrot & repair
« Reply #2 on: April 22, 2014, 06:43:55 PM »

Very interesting.  :)

Just one quick query, please. What did you use as the input to ddrescue? The individual JPEG files? The raw CD image? Or . . ?  :-\

/dev/cdrom, the raw device.   All defaults, just input from the raw cdrom & output to a file, you end up with a file similar to what dd would have given you of the original disk had been healthy.

With hindsight I probably ought to have used some more sensible parameters like a logfile but I decided that, since it might take a while, it was best to get something started while I read the manual at my liesure.    Then, since it seemed to be doing good things, I just let it continue.
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burakkucat

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Re: CD Bitrot & repair
« Reply #3 on: April 22, 2014, 08:36:22 PM »

Thank you. That makes sense.  :)
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kitz

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Re: CD Bitrot & repair
« Reply #4 on: April 22, 2014, 10:37:03 PM »

Quote
A huge success then, though I say it myself. 
Yes indeed.   Well done to you and ddrescue
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