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We've run into a weird issue today when copying files from a Windows Server 2008 R2 (SP1) to a Windows 7 Prof. client. If I initiate the transfer from the Server 2008 box I'll get 80-100MB/sec which seems to be what I'm expecting. As soon as I initiate the transfer from the Windows 7 client end then I'm getting speeds closer to 40-45MB/sec. We've created a Ramdisk to avoid seeing limitations from the local storage for the tests. This was consistent over multiple runs.

The test file is about 3GB in size.

I also don't think that it should be related to caching. I created the files with different sizes for every run to be sure that I'm not seeing any caching effects.

Any explanation for that?

Thank you, Felix

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I also should add the I always copied from the server to the Windows 7 box. One time from the Server raid to the ram disk on the Windows box started from the server GUI. The other time I initiated the transfer from the Windows 7 box. – Felix Mar 29 '12 at 6:07
How about AV software configurations, not likely to cause a 50% drop in performance but who knows. Out of the box on win7/w2k8r2 I've always seen the 80-100MB/s, you pretty much have to go out of you way to screw this up. – tony roth Mar 29 '12 at 13:27

You might be seeing some effects of a slowdown due to SMB NOTIFY calls which induce transmission delays when using Windows Explorer to display the remote directory's contents while copying. You might try using a different copy tool without involving Explorer altogether (xcopy, robocopy) or closing the Explorer remote directory window after starting the copy process.

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Try adjusting the TCP chimney and receive window scaling settings on both the 2008 and Windows 7 box. It can cause strange behaviour in some situations.

I'd start with the receive window scaling. Run this in an elevated prompt one one, then the other, then both machines and see if it makes a difference in each case:

netsh int tcp set global autotuninglevel=disabled

set it to 'normal' to reset to default.

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