Trying to understand Copy Failures

[Seeker47]

and the possible ramifications thereof.

This is happening on a desktop system running W7U x64, with 8 Gb. of RAM. I don't recall seeing this happen on any of my other computers, but I'm not certain about that.

After copying a file (this is usually to a portable external drive), if the file is important I may do a file compare between the source and the copy. I do this either using a built-in feature of my file manager program or one of a few separate utilities such as HashCalc. I particularly like that one, which gives you up to 10 comparisons at once, although I just have MD5, CRC32, and SHA1 enabled. I seem to be getting something like a 20% failure rate on the comparisons. Typical files compared could be anything from a 1 Gb. VOB file to a 17 Gb. MKV file. I always do the compare for my Acronis TI image files, which can run up to 87 Gb., because a copy of those absolutely must be identical, or else it could be worthless. It may be that the larger the file is, the greater the chance of a failure on the file compare.

If I re-copy a file that failed compare, there is a pretty good chance that the subsequent attempt compares successfully, although sometimes multiple re-dos may be required until there is a certifiably good copy.

I'm somewhat confident that this has not been happening on another computer that is running W7 x86 with 4 Gb. of RAM, or on a couple laptops. (But the copying or comparing is much slower there, because there is much less RAM.)

My first question is: What are the likely causes of this, on the affected computer ? Someone is probably going to suggest that the Buffalo RAM on this computer is suspect . . . but then, would there not be some other clear symptoms, in the routine usage of various apps ?

My follow-up question is: How much does this matter, for video files ? I have played the "failed" copies of quite a few video files -- .Avi, .Mkv, .Wmv, whatever -- or in the form of VOB files from a DVD structure, and they all still seem to play normally, at least in desktop players like VLC or MPC-BE. I'm not detecting anything wrong there, even as to language tracks or subtitles. I think they would also play normally from my WD-Live, though I need to confirm that. So, is there a fair amount of "give" in the exactitude of video files, such that they don't have to be perfect copies in order to work ?

[El Heggunte]

Looks like you still haven't read the topic below:

https://forum.videohelp.com/threads/367509-Files-corrupted-when-copying-to-external-usb3-hdd

[Seeker47]

Looks like you still haven't read the topic below:

https://forum.videohelp.com/threads/367509-Files-corrupted-when-copying-to-external-usb3-hdd

Thanks for that.

No, I've been dealing with this problem for some time now, but that discussion was news to me. (Last post in that thread was in Q3 of last year, but if I have things to add -- after this -- I would probably do so there.)

So far, I've read about 2/3 of that thread and skimmed the outside links from it. I don't believe the culprit was cabling or anything else in the hardware realm. If it was something like a RAM issue, I just don't believe the effects would be this specific, this isolated. I'm using back ports off of that computer, which are USB-2; this issue also occurs over e-SATA, though perhaps less often. It makes a lot more sense to me that this is some flaw in 64-bit W7, or else I would surely have noticed it on the other systems running 32-bit W7. I will try the countermeasures suggested, starting with Teracopy.

None of this discussion really addresses my second question, as to whether there is flexibility or margin-for-error in the exactness of copied video files. My empirical observation is that there is.

[Keyser]

None of this discussion really addresses my second question, as to whether there is flexibility or margin-for-error in the exactness of copied video files. My empirical observation is that there is.

There is no such thing as flexibility or margin for error when it comes to copying files. A copy operation must be 100% accurate, period. Even a single bit change can be catastrophic. Of course, that all depends on what part of the file is affected. In an executable file, for example, if there are errors in executable code itself, the results can be very serious; on the other hand, if it occurs in some data structure, it may just mean that some word is spelled wrong.

The same applies to video files. Depending on what part is affected, you may have some small unnoticeable change or you can end up with an unplayable file.