Windows 11 Insider 22449 update for SMB compression
Published Sep 14 2021 04:04 PM 4,964 Views

Heya folks, Ned here again. We released a change to SMB compression for Windows 11 Insider Preview build 22449 & later



We stopped being so algorithmically cute: when you request compression, we now just try to do it because you said so. :) 


Full explanation

We first introduced SMB compression in Windows Server 2022 & Windows 11. SMB compression allows an administrator, user, or application to request compression of files as they transfer over the network. This removes the need to first deflate a file manually with an application, copy it, then inflate on the destination PC. Compressed files will consume less network bandwidth and take less time to transfer, at the cost of slightly increased CPU usage during transfers.


Based on testing and analysis, we have changed the default behavior of compression. Previously, the SMB compression decision algorithm would attempt to compress the first 524,288,000 bytes (500MiB) of a file during transfer and track that at least 104,857,600 bytes (100MiB) compressed within that 500-MB range. If fewer than 100 MiB were compressible, SMB compression stopped trying to compress the rest of the file. If at least 100 MiB compressed, SMB compression attempted to compress the rest of the file. This is of course impossible for any normal user to understand. 


Starting in Build 22449, we will no longer use this decision algorithm by default. Instead, if compression is requested, we will always attempt to compress. If you wish to modify this new behavior to return to a decision algorithm, read SMB compression behavior & settings changes - Microsoft Tech Community.


Please use the Feedback Hub to give feedback or report issues with SMB compression, using the Files, Folders, and Online Storage > File Sharing category.


Until next time,


Ned "smooooosh" Pyle

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Last update:
‎Sep 01 2022 03:54 PM
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