RoboCopy supports Copying Files over SMB with Compression on Windows Server 2019, and beyond

Windows Server

Microsoft is working hard to add features to Windows Server vNext, but is not forgetting about the vast majority of organizations that run Windows Server 2019 and might like the same functionality.

The feature that I want to discuss with you today is SMB compression with robocopy.exe.

SMB Compression with Robocopy

The announcement for Windows Server vNext Insider Preview version 20206 mentions that Microsoft added the /compress command switch to robocopy.exe.

When using this switch, If the destination computer supports SMB compression and the files being copied are compressible, you should see significant performance improvements.

When the command switch is used, the SMB Compression functionality adds inline whitespace compression to file transfers, removing congestion and copy time. Depending on the (in)efficiency of file formats and the IO pattern, the performance increase in copies can be up to fourfold.

SMB Compression uses a negotiation mechanism, so multiple compression algorithms are possible, and vendors can add their own. Currently the list is XPRESS (also known as LZ77), XPRESS Huffman (LZ77+Huffman) and LZNT1.


Ironically, Microsoft released Windows Server vNext Insider Preview version 20206 on September 2nd, 2020 and released KB4571748, for Windows Server 2019 on August 20th, 2020. This means that Windows Server 2019 gained the functionality even earlier than the Preview build.

Windows 10 hasn’t got the SMB Compression functionality rolled out yet, but is slated to have support for it through updates, too.

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