Slower SMB Read Performance for large files in 22H2

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. We're working with another team to understand this and have them get a permanent fix to you.

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

Ned Pyle

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