Large files consistently get corrupted

I've been having weird problems on my PC with files getting corrupted and can't figure out where the problem is. It happened when I had Windows XP on here, and it still happens with Ubuntu, so it's not a driver issue. I'm thinking there's a piece of broken hardware somewhere.

I just noticed that if I do an md5sum on a large file (a few GB) twice in a row, I always get different results. However, if I do an md5sum on small files, the results are the same (I did a loop 10,000 times on a 300k file as a test. Checksum never changed).

My first thought was my HDD was bad, but the SMART tests came back clean, as well as an fsck in Ubuntu / check disk in Windows. Weird thing is it happens on large files on two other hard drives in my system, too. The odds of having three bad drives (2 PATA, 1 SATA) seems small, so I'm thinking the problem is not the HDDs.

Memtest86+ ran without errors, so I don't think it's my RAM.

I also ran Stress and StressCPU tests from the Ultimate Boot CD and they didn't report any errors. Tried the Mersenne Prime Test, too, and no issues there. Would these tests rule out what's causing my problems for sure? I have no problems with smaller files, so I'm worried that this doesn't rule out my CPU.

So my thoughts are that it's either the CPU or the motherboard. Any ideas how to figure out which is the bad apple?

Any ideas on what to look at next?
7 answers Last reply
More about large files consistently corrupted
  1. Run some other HDD tests. I don't know the new ones, I remember those

    http://www.seagate.com/www/en-us/support/downloads/seatools
    http://www.hdtune.com/
  2. As an update, the files it corrupts are about 850MB or bigger. I was wondering if there might be a magic 1GB size limit before corruption begins, but nope, it's lower.

    By the way, diff also says that the files (original and copy) are different. Makes me think it's not the arithmetic of md5sum that's getting messed up.
  3. I just had the opportunity to drop in a replacement CPU. md5sums still change all the time, so it isn't the CPU.

    Tried one of the hard drives in another computer and the md5sums were consistent. Not the hard drive.

    I guess that leaves the motherboard.
  4. It can't be the mobo from what I know, the RAM is more likely. For large filres from the Internet it can be the browser or the firewall as well.
  5. mosox said:
    It can't be the mobo from what I know, the RAM is more likely. For large filres from the Internet it can be the browser or the firewall as well.


    Why not the motherboard? md5sum moves data from the HDD, through the southbridge, through the northbridge, into RAM and finally into the CPU for processing in the ALU.
  6. I know but never heard of data corruption in a mobo but a lot of it in the RAM. I might be wrong though. Try with only one stick of RAM at a time, maybe one of them is bad.
  7. I managed to get out and buy a new motherboard. Now, the md5sum results are always the same for large files. It was indeed a motherboard problem. At least I know for sure that my mysterious problems will disappear!
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