Crc Errors In Cd

I've always feared the words "Cyclic Redundancy Check". More so because of the word "error" which always proceeds. Handling the CDs gently has always been my top priority and I can proudly say that my discs have very less amount of scratches on them. Recently, I backed one of my ageing DVD discs up @ 4 CDs. The master copy finally gave up and was rendered useless. Proud as I was, having backed up the old stuff. To my surprise, when I tried to restore the data through the backups (which have been as new as ever), the disgusting CRC error turned up on one of the discs. Despite very close examination of the disc, I couldn't find any signs of a scratch. I tried all kinds of recovery softwares, but the results were dismal. The file being a .rar spanned over the four discs, could not be used one bit.

I have an idea, but am not sure, how good it would be. Anyways, here it goes.

> Read all the readable sectors and as much as possible of the unreadable ones.
> Try all possible combinations of byte values (0-255) for each unreadable position, until the MD5 cheksum of the file matches.

What do you say guys, would it work and would it be feasible to try all the possible byte values?

 

 

 

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Amazingly, I was able to recover the data completely. Here's what I did:-

STEP 1: Since the file could not be copied or extracted directly, I tried to use the recovery feature in WinRAR to save the repaired file. WinRAR kept reading the disc for hours, eating up all the CPU resources, but we were going nowhere. So, I had to cancel the process.
STEP 2: I downloaded the application CDCheck from http://www.kvipu.com/CDCheck/ and used it to recover the file.
STEP 3: Although, CDCheck was able to save the file locally, this file was not without errors and the compressed archive couldn't be extracted.
STEP 4: It occured to me, that I had the 'Add Recovery Record' option turned on while making the archive. The recovery record was no more than 1% of the size of the archive. But it sure turned out to be handy, as the file was completely recovered.

Kudos to both of these softwares!

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I guess you are talking about the recovery record that is optional with RAR and not something related to your CD burner. I have rarely been able to get a CD with a CRC to work. Sometimes a little spit and elbow grease does the trick. I have also considered buying one of those scratch removers but I usually decide to instead to burn 3 more copies that what is needed. On a side note I have discovered the hard way that CDs will not last forever. I dug up some from around 10 years ago and the film that holds the data just crumbled in my hands.

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I don't gently handle mine and they work

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It is related to the CD burner. The File has read errors in 23 sectors which renders it uncopyable. WinRAR can recover files using the recovery record. But, its only possible if the file can be read from the CD. CDCheck does the same by reading whatever's possible and padding the rest up.



You are correct about the unrecoverability of the CD with CRC errors. The only way I have managed to get them to work is on a brand new drive. Scratch removers aye, sounds interesting. I'll try my hands on them.



And to think, that mortality was a trait exhibited by the living things alone. I guess, the good ol' HDDs are the most trusty ones, when it comes to data longevity. What do you think?



Sometimes, even the disc where finding a scratchless area is tough, seems to work as a breeze. That's probably because of a high quality reader and using high quality CDs.

 

 

 

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Something that does help is slowing down the read speed of your cd-rom drive (using a tool like cd-bremse). This is what windows does for you when it encounters a lot of CRC errors on a cd.

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