Is a copied file corrupt or is the crc corrupt?

  enonod 10:12 21 May 2009

I have had immense trouble copying large, 8-10GB, files to external disk via USB 2. The file is validated by the originating program as OK on the internal source drive. On arrival at the destination the file is the same size but defined as corrupt by the originating program's validator.

If it is possible for the file to corrupt on the journey, is it not possible that the file did not corrupt but the subsequent validation (of CRC?) over the same connection could be corrupt, since the file must be read back over that connection?

The answer would seem logically to be yes! Therefore how can this be a reliable test?

Does anybody know of a program that will copy a file and check the CRC as it does so and then ask for the block to be resent until it is error free and then continue with the rest?

  AndySD 11:29 21 May 2009

There is one further option you might want to consider, The external disk itself has a problem. You may want to error check this first.

  enonod 11:45 21 May 2009

Thank you AndySD. Yes I have checked the NTFS disk for bad blocks and it reports as fine. It does work OK on ordinary small multi-file/folder copy, it is only multi GB file copies.

  AndySD 13:38 21 May 2009

Have you tried using MD5 checksum verification on the files just to confirm the program is working correctly?

  Peter 17:13 21 May 2009


Have you checked your memory (RAM). I had a problem with one computer where copying files up to about 5 Meg was okay, but 50 Meg copies often had just 1 byte corrupted. I checked the source and destination drives, but could find no problem so I checked the RAM. On first testing it, no problem showed up, but more in-depth testing highlighted a problem with one stick of RAM. Eventually I replaced all the memory and the problem hasn't shown up again.

There is a Microsoft memory tester available free from their website, which you can download and boot the machine into to test your RAM at different levels of depth. Proper testing can take quite a long time, but it is worthwhile.


  enonod 17:49 21 May 2009

Thank you Peter, I will give that a try if I can find it, It is about the only thing not checked.

  enonod 19:15 21 May 2009

Thank you all for your assistance. I have obtained another USB drive and using the same port and cable, this works perfectly every time.
I guess it is back to WD, though it tested Ok as far as can be done.

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