Microsoft Finally Fixed SMB Copying Speeds On Windows 11
Look For KB5022913 Under Optional Updates
Windows 11, version 22H2 came with an unexpected and unwanted surprise, decreased performance when copying large files from a remote machine or server. For those that updated Windows, SMB copying speeds could plummet for many remote copy sessions and occasionally with local copying as well. We never received official notification of the actual impact but for those affected by the issue they saw a 50% increase in copying times.
The new patch was tested in Windows 11 Preview Build 25252 and resolved the issue without any negative effects. That lead to the release of KB5022913, which you can test now via Windows Update. If you have any concerns you should start your testing now as it will be distributed to everyone next month on Patch Tuesday.
If you want to avoid this altogether, make use of robocopy and xcopy as they do not use buffered I/O and so the issue does not effect them at all. Bleeping Computer has more details and some history on this unfortunate bug, if you are interested.