Verifying files by check sum / content after transferring unreliable - how to check?

Is verifying files by check sum / content after transferring (copying, moving) indeed unreliable?

Since "ever" I - if I checked files at all - checked files by content or check sum after transferring them, so this information sounds very astonishing to me now, I hadn't had any clue about what I read here: http://blogs.msdn.com/b/oldnewthing/archive/2012/09/19/10350645.aspx

Obviously meaning in many cases checking files by content / check sum checks the data in the buffer, if I see it right.

So, is it like that? Does it refer to all of the synchronizing / backup / copying, check sum, etc. programs?

And what is the best / easiest way to (automatically) check files after transferring. E.g. when copying all of the files of a 4TB drive to another one.

 

Re: Verifying files by check sum / content after transferring unreliable - how to che

Kletus...

I'm not in my league with this, but could this make sense?

I think the article is referring to times when you are seeking to verify data across a network span between two systems (operating systems), where system b (copy destination) requests a checksum from system a (file original location). I believe the author is saying that in that particular situation checksums would be created from the cache/buffer on both computers. In the case of you copying to a secondary disk connected to a single computer I think the checksum should work fine. Sounds like one of those programmer's dilemmas to me.

Sorry if I am off on this. I know you are looking for some programming expertise. I'll just say that reading this, it made sense to me about the author's comments:

Does seem to me logical to have system b create the checksum for verification from its "copy" of the file/data when it comes to a network transfer...

Hope I'm not way off about this.

 

Re: Verifying files by check sum / content after transferring unreliable - how to che

The basic question here - how can we be certain files have copied correctly - is one I've often wondered about, though I've never seen any evidence to the contrary. I have had to assume Windows validates copies somehow, but can Adrynaline or anyone give us more info about that?

 

Re: Verifying files by check sum / content after transferring unreliable - how to che

Hello AtlBo,

Thank you very much.

Some days ago, I would have answered, no it doesn't or something like that although I do not have any clue about anything.

Well, actually, yes I am, but actually I do have seen one (I couldn't believe what I meant to understand, may be I didn't get that right): http://sourceforge.net/p/freefilesync/discussion/help/thread/449aaaf9

It is the developer of FreeFileSync, the best snync program I know. And if he does not know who else should?

Yes, that sounds plausible. And I assume the procedure will work correctly.

Actually my post mainly shall refer to copying / moving files to / from / on computer / external drives. So for example moving files form an external 4 TB USB 2.0 drive to another one.

No, no, not at all, I am very happy about knowing your opinion.

Yes, indeed, that's absolutely right.

Sorry, I am not quite sure, what is the contrary here?

No, it does not (if I am right), at least it does not check by check sum or content. Checking by one of those would make transferring files half the long longer or as long as transferring, if I see it right.

Many thanks again

 

Re: Verifying files by check sum / content after transferring unreliable - how to che

Kletus,
Have a look at WinDataReflector. It might be what you're looking for.

http://www.majorgeeks.com/files/details/windatareflector.html

 

Re: Verifying files by check sum / content after transferring unreliable - how to che

Hello Eldon,

Thank you for that program, the link, yes, a good idea, I had tried it some days ago, it is not that fast obviously, with less options, if I remember it right, FreeFileSync is very much faster (the fastest one I know) and does also check by content (not by CRC / check sum), but it (actually) should have the same effect, so to check the correct transfer, respectively a compare by bit.

Copying files here with a USB 2.0 system only doing this from a full external 4TB drive to another one lasts 2½ days (running 7/24), checking by content or CRC about the same time. So about 5 days just for transferring, if it runs without any problems.

And even when using WinDataReflector the core problem (if it really is one) stays the same, I guess.

Many thanks again.