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Trying To Explain Cd Corruption


LBonser

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Okay, here's the situation:

 

Say you have about 2200 source code files. Spread across a handful of subfolders and varying numbers of subfolders in each of those.

 

They were burned to a CD, and when you do a visual compare in Windows Explorer between the files on the CD and the same files on a hard drive, they appear to be the same. Same filenames, same file sizes, modification dates/times.

 

However, if you run a file compare (say windiff), you notice that about 2/3rds of the files are coming up different.

 

Look in one of the subfolders. There are say 5 files: a.h (2k in size), b.h (16 kb), c.h (10 kb), and so forth.

 

If you look at a file in the subfolder, say "a.h" (C language header file) and open it in a text editor, you discover it's really the text from "b.h". At least only the first 2kb of it. Open b.h and it's the rest of the b.h file (resuming exactly where the previous file left off), plus at the end, a bit of the top of c.h.

 

It's like the bytes are all there, but "shifted" onto the next sector. The degree of "shifting" appears to be about 1680 bytes.

 

The CD was probably created with Roxio CD Creator version 6 (yeah, an old version--it's what was installed on the PC). Don't have details on the CD drive manufacturer. Under Windows 2000 or XP (don't know for sure--the person that did the original burning is long gone from the company).

 

Has anyone seen anything like this before? And if so, did you ever figure out a reason why?

 

I remember a lifetime ago (early days of MS-DOS) seeing similar issues on floppy disks when the FAT table would get scrambled, but never on a CD.

 

I work in Compliance for a manufacturing company in a HIGHLY regulated industry and I've inherited this problem. I now have to explain how it happened to a (non-technical) regulator or the company faces potentially huge fines. The regulator isn't buying just "the CD was corrupted when it was created."

 

Thanks in advance for any assistance.

 

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A lot would be down to how the disc was created - if it was (as I suspect) made using Drag to Disc (packet writing) corruption is not unknown. Basically what could have happened is that someone formatted it and treated it as a 'dirty big floppy' and simply dragged the files over.

 

Add to that that, if it was a RW disc, then the dye sublimate used on those tends to deteriorate over time (it's a lot more amorphous than the dye sublimate used in -R discs due to the fact that it has to be able to be wiped) so, over time, it can leech out and data gets lost.

 

We're forever telling people here never to trust D2D or RW discs for any serious backup

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