Windows 11’s “Compress File Aggressively” behavior applies to files while they travel over an SMB network connection; it does not permanently compress the source file on disk. On updated Windows 11, when a client or server requests SMB compression, Windows attempts it across the requested file without the original sampling cutoff. Use a client-wide setting for all suitable transfers, a share or mapped-drive setting for a narrower scope, or a copy command for a single job. Compression is most useful when the data can shrink and network bandwidth is the bottleneck.
What “Compress File Aggressively” means
SMB compression is a transfer-time feature. It can reduce the amount of data sent across a network, potentially shortening transfer time while using additional CPU. It does not change the file’s stored format or make a permanent compressed copy.
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The phrase “aggressively” refers to whether Windows samples part of a file before deciding to continue compressing it. In the original behavior, SMB tested the first 500 MiB (524,288,000 bytes). If at least 100 MiB (104,857,600 bytes) compressed, it continued attempting compression; if less compressed, it stopped for the rest of that file. Following Windows 11 update KB5016691 (OS build 22000.918) and Windows Server 2022 update KB5016693 (OS build 20348.946), Microsoft documents that SMB attempts compression without sampling by default when compression is requested. This does not guarantee a faster copy: incompressible data can still cost CPU without meaningfully reducing network traffic. Microsoft’s SMB Compression documentation describes the current behavior.
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Choose where to request compression
Pick the narrowest scope that matches the task. A client setting applies to transfers initiated from that computer; a server setting or share flag controls requests from the server side; mapping and copy options are useful when you want to target a connection or operation.
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| Scope | How to request it | Use when |
|---|---|---|
| Client-wide | Group Policy or Set-SmbClientConfiguration -RequestCompression $true |
You want the client to request compression generally. |
| Server-wide | Group Policy or Set-SmbServerConfiguration -RequestCompression $true |
You administer the server and want it to request compression across shares. |
| One share | New-SmbShare or Set-SmbShare with -CompressData $true |
You want to configure a particular share rather than the whole server. |
| One mapped connection | New-SmbMapping with -CompressNetworkTraffic $true, or NET USE with /REQUESTCOMPRESSION:YES |
You want compression associated with a mapped drive. |
| One copy operation | Robocopy or Xcopy with /COMPRESS |
You want to request it for a specific copy job. |
These options are documented in Microsoft’s SMB Compression guidance. File Explorer, applications, and third-party copy tools need a compressed mapping, a share configured for compression, or an always-compress client setting to use it.
Set compression on a Windows 11 client
Use Group Policy
- Open the Local Group Policy Editor or the relevant domain policy editor.
- Go to Computer Configuration > Policies > Administrative Templates > Network > Lanman Workstation.
- Enable Use SMB Compression by Default.
Use elevated PowerShell
Run PowerShell as an administrator and enter:
Set-SmbClientConfiguration -RequestCompression $true
To stop the client from requesting compression, Microsoft documents:
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Set-SmbClientConfiguration -DisableCompression $true
The corresponding policy is Disable SMB Compression. The client configuration reference explains the relevant switches and sampling option: Set-SmbClientConfiguration.
Configure requests on a server or share
Request compression across server shares
In Group Policy, go to Computer Configuration > Policies > Administrative Templates > Network > Lanman Server and enable Request traffic compression for all shares. Alternatively, from elevated PowerShell, run:
Set-SmbServerConfiguration -RequestCompression $true
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Set compression for one share
When creating a share, include -CompressData $true:
New-SmbShare -Name "Sales" -Path "C:sales" -CompressData $true
For an existing share, run:
Set-SmbShare -Name "Sales" -CompressData $true
Microsoft says these SMB configuration changes take effect immediately without a reboot. Confirm that the intended client or share is the one requesting compression before applying a broad setting. Microsoft’s configuration examples cover both scopes.
Request compression for a mapping or a single copy
Mapped drive
To create a mapped drive that requests compressed network traffic, use elevated PowerShell:
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From Command Prompt, the documented alternative is:
NET USE * \fs1.corp.contoso.comsales /REQUESTCOMPRESSION:YES
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One-off copy
Add /COMPRESS to a Robocopy or Xcopy command to request compression for that copy. For example:
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These options request compression; they do not override the limits of the data or the network. Refer to Microsoft’s SMB Compression documentation for the tool-specific behavior.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When compression helps—and when it does not
Compression is most promising when the network link is constrained and the data has patterns that compress well. Microsoft identifies VM disks, ISO images, and dump files as examples of suitable data. ZIP, 7z, and RAR archives, as well as common compressed audio and video formats such as MP3, FLAC, MP4, and MKV, generally do not gain significant performance from SMB compression.
- Likely candidate: large, compressible data crossing a lower-bandwidth link.
- Unlikely candidate: already-compressed archives or media, or a transfer limited by storage throughput rather than network bandwidth.
- Possible trade-off: additional CPU work for little or no reduction in bytes sent.
Microsoft’s slow-transfer guidance gives approximate storage throughput requirements of 110 MB/s per 1 Gbps, 1.1 GB/s per 10 Gbps, and 11 GB/s per 100 Gbps, assuming no other bottleneck. These are troubleshooting estimates, not guaranteed SMB transfer speeds. If storage cannot sustain the rate implied by the network, enabling compression may not solve the problem. See Microsoft’s SMB slow-transfer troubleshooting guidance.
Sampling controls and Windows versions
On the updated Windows releases described above, no sampling is the default when a client or server requests compression. The EnableCompressibilitySampling option in the client configuration reference re-enables sampling. When sampling is enabled without explicitly specified thresholds, Microsoft documents the original example: test the first 500 MiB and continue only if at least 100 MiB compresses. This is a behavior control, not a universally recommended performance setting; changing thresholds does not guarantee faster transfers.
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11SMB compression is supported on Windows 11 and Windows Server 2022 or later. Microsoft’s feature overview lists XPRESS (LZ77), XPRESS Huffman, LZNT1, and PATTERN_V1 for Windows 11 and Windows Server 2022 and later. LZ4 is listed for Windows 11 version 24H2 and later and Windows Server 2025 and later; Windows negotiates an available algorithm supported by both ends. See Microsoft’s SMB feature overview.
Compatibility limits and troubleshooting
SMB compression supports SMB signing, encryption, SMB over QUIC, and SMB Multichannel, but not SMB Direct over RDMA. Windows does not compress SMB messages over RDMA. The protocol behavior reference is available at Microsoft’s MS-SMB2 specification.
Quick Recap
- If a transfer is not compressing, check whether compression is requested at the client, server/share, mapping, or copy-operation scope you chose.
- If a copy is no faster, check whether the file is already compressed and whether storage or CPU, rather than network bandwidth, is the limiting resource.
- Before deploying a policy broadly, verify that the setting and cmdlet are available on the Windows builds in use.
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