Slower SMB Read Performance for large files in 22H2

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This post has been republished via RSS; it originally appeared at: New blog articles in Microsoft Tech Community.

Heya folks, Ned here again. There is a performance regression in 22H2 when copying larger files from a remote computer down to a Windows 11 computer. A large (multi-GB file) might see as much as 40% less throughput over SMB when copying down (reading). Copying that same file to a non-22H2 machine (writing) won't see this problem.  


For a workaround, use robocopy or xcopy with the /J (unbuffered IO) parameter. For example:


robocopy \\someserver\someshare c:\somefolder somefile.ned /J


That will return your performance to 22H1 throughput. The issue is not actually in SMB code, so I can't give you an ETA for a permanent fix yet; SMB is just the most likely scenario to be noticed. You could see this behavior even with local file copies not using SMB. We're working with another team to understand this and get to a permanent solution.


I will update this post with more info when I know more. Thanks for your patience.


Ned Pyle

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