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Storage at Microsoft
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Slower SMB read performance for large files in 22H2

NedPyle's avatar
NedPyle
Former Employee
Oct 03, 2022

Heya folks, Ned here again. There is a performance reduction in 22H2 when copying larger files from a remote computer down to a Windows 11 computer or when copying from any Windows computer to a remote Windows 11 computer. 

 

Fix update 03/06/2023: update February 28, 2023—KB5022913 (OS Build 22621.1344) Preview - Microsoft Support contains the kernel update that fixes this issue. 

 

For the latest information about this issue, please see the known issues section of KB5017389

If you are using Microsoft 365 admin center and have Windows Release Health available there, you can view this issue in the Windows 11, version 22H2 section. The ID on Microsoft 365 is WI442499.

Updated Mar 06, 2023
Version 10.0

103 Comments

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  • NedPyle's avatar
    NedPyle
    Former Employee
    Oct 04, 2022

    I can't share too many details yet, but we know exactly where it is getting slower in Kernel, nothing to do with SMB or compression. 

  • Karl-WE's avatar
    Karl-WE
    MVP
    Oct 04, 2022

    Hi NedPyle thanks for letting us know.

     

    May I share some thoughts and questions? 

     

    1. Could it be the "lazy-writeback", introed and enabled by default since 1809 builds could be a cause?

     

    Even when not utilizing SMB over network but usual local copy jobs e. g. from / two nvme one might notice a massive jigsaw effect when copying solid bigger files, especially with File Explorer, not so much with Robocopy as of its nature of multithreading.

    Unfortunately there is no flag such as ADMX / CSP to disable lazy write-back for Explorer, to revert to the default behaviour of Windows Client and Server versions before build 1809.

    The fact unbuffered IO does help, could be indicating this. 

     

    2. Could you exlude the now wider default use of SMB compression, to be a potential cause for the issue?