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Robocopy verification

Posted on 2007-12-01
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Last Modified: 2011-12-23
I'm trying to ensure that robocopy does verification after it copies files.

I've seen plenty of post from folks saying that it does, but I have
yet to see any sort of documentation for this.
I'm looking for something definitive (preferably from MS). I've been
all over E-E, the MS Knowledge base, msdn, technet,
& mvps.org (to name a few), but no solid confirmation. I've reviewed
the .doc for robocopy which is included with
the resource kit download...nothing.

I'd like an answer ASAP, so I'm giving 500 points on this one...

Any help with this would be greatly appreciated.
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Question by:IntInc
5 Comments
 
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Expert Comment

by:weellio
ID: 20390279
the latest version has a progress bar,. you can turn on verbose logging to see the results

http://www.mydigitallife.info/2007/05/07/robocopy-syntax-command-line-switches-and-examples/
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by:
souseran earned 400 total points
ID: 20390576
Robocopy does NOT write-verify. However, apparently it can be included in a script which will allow this.

See this March 2001 WindowsITPRO article, Real-World Scripting: Data Migration with Robocopy, Part 1 for more information:

http://emea.windowsitpro.com/WindowsScripting/Article/ArticleID/19826/19826.html

If write-verification is a function you need, XXCOPY DOES write-verify. It can be found here:

http://www.xxcopy.com
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Expert Comment

by:Malli Boppe
ID: 20390690
Robocopy doesnot have a verify option.only option that you have is to create a log which can used to verify if the files are copied.
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Assisted Solution

by:oBdA
oBdA earned 100 total points
ID: 20392526
If at all, you only need a verify if you're copying to unreliable media (floppy, CD, DVD, USB, tape, ...). If you're using robocopy only to copy from one server to the next, I don't see the need to run a verify (and I've copied literally hundreds of gigabytes using robocopy, without any problems and without verify).
It's not the job of a high-level copy program like robocopy to verify that the data has been written correctly; unlike copy programs written for DOS (where verify actually was an issue), robocopy uses standard Windows APIs. If those APIs report that the data has been written correctly, why would there be a need for robocopy to re-check this? It would use the same APIs that just reported that everything was okay, and so, in all likelihood, just waste your, the CPU's and the IO system's time.
Another matter are low-level copy programs like CD/DVD writing software, but that's not the issue here.
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Author Comment

by:IntInc
ID: 20393405
Thanks everyone for your answers. Our question is answered, but I'm curious how everyone knows -- we looked around but couldn't find confirmation one way or the other.

oBdA: I think that's an interesting point about the Windows API. Given that Robocopy does not verify, I would use it whenever I would use Explorer's Copy, which I do not use it for more critical tasks:
 - How many of those 100s of GB had errors? How do you know? Maybe it was a few files, and the users haven't accessed them yet; or maybe they did encounter a corrupted or missing file months later, but how could the cause be attributed to robocopy? Was a missing file accidently deleted, misplaced, or under a different name ...? Did Word corrupt it? Our policy is to not believe anything we haven't verified.
 - I've seen the standard Windows copy function do some odd things, especially on large copy jobs.
 - I agree that verification will likely wasted I/O and CPU -- an error is very unlikely and I hope it's a complete waste -- but it's worthwhile to use given the cost of dataloss.

I'll accept souseran, who answered the question first. oBdA's answer definitely added value -- my statements above are partly just a difference of opinion and party depend on circumstances oBdA couldn't have known. Thanks again to both of you.
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