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Different drives, different Crc, no read or verify errors


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4 replies to this topic

#1 baronluigi

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Posted 19 April 2017 - 07:31 PM

I made an ISO image from an unprotected DVD movie disk. I have copied the disk twice, without receiving any error neither in the copy proccess nor in the verification. Each copy ( and its respective verification) was made in a different drive and computer.

However, the CRC I get of each ISO is different. How is this posible? Does this mean that the copies are damaged?

I did not posted the logs because I thought there was no point in doing so, due to nothing out of ordinary appears in them.

Edited by baronluigi, 19 April 2017 - 07:38 PM.


#2 dbminter

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Posted 19 April 2017 - 09:41 PM

Could be down to how each of the different drives in the different PC's "reads" the data?  Maybe one drive does some kind of data reading that the other doesn't?

 

 

As long as the discs read to an image, I wouldn't be too worried about differing CRC's.  If you're really worried, then watch the discs' contents in a DVD player.  If they play fine, then I wouldn't worry.  There are so many other things in life to worry about. =))



#3 baronluigi

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Posted 19 April 2017 - 10:09 PM

Could be down to how each of the different drives in the different PC's "reads" the data?  Maybe one drive does some kind of data reading that the other doesn't?

 

 

As long as the discs read to an image, I wouldn't be too worried about differing CRC's.  If you're really worried, then watch the discs' contents in a DVD player.  If they play fine, then I wouldn't worry.  There are so many other things in life to worry about. =))

 

To be honest, I could consider myself a kind of paranoid regarding to this kind of matter. Yeah, the content of the ISO is fully playable but this crc difference makes me wonder if there is some kind of video data missing.

 

Related to this, there have been times that while I have not received any error when creating a ISO, I receive misscompare error messages when I verify that ISO image against the disc inside the drive. I cannot understand why either.

 

The disc has some skratches, could this missmatch be caused by this?


Edited by baronluigi, 19 April 2017 - 11:41 PM.


#4 dbminter

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Posted 19 April 2017 - 10:28 PM

What I can't understand is a burn that completes, a Verify that completes, and the disc is STILL unreadable.  Yes, I've had that happen before.  I also fail to see how a burn can complete but the Verify fails.  I would think if the data is corrupt when it's written, why doesn't the write fail?  For instance, on DVD+R DL's, when drives fail, they will write them fine but fail Verify at the layer change.  But, that's the nature of the beast.  :unknown:



#5 baronluigi

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Posted 19 April 2017 - 10:33 PM

What I can't understand is a burn that completes, a Verify that completes, and the disc is STILL unreadable.  Yes, I've had that happen before.  I also fail to see how a burn can complete but the Verify fails.  I would think if the data is corrupt when it's written, why doesn't the write fail?  For instance, on DVD+R DL's, when drives fail, they will write them fine but fail Verify at the layer change.  But, that's the nature of the beast.  :unknown:

 

In this kind, the disc I am using as source is a retail pressed disk, not a burned disk.

 

I have made another copy, using another unprotected disk as well, and this time I have obtained the same CRC in both copies.


Edited by baronluigi, 19 April 2017 - 11:21 PM.





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