The Microsoft.Build.CopyOnWrite MSBuild SDK overrides the native MSBuild Copy task to add support for ReFS CloneFile (Copy on Write). It is designed to be as backwards compatible as possible and should directly replace all usages of Copy in MSBuild.
This is intended to be used in a large repo already onboarded to Central Package Management. In your Directory.Packages.props:
<Project>
<ItemGroup>
<!-- <PackageVersion> elements here -->
</ItemGroup>
<ItemGroup>
<GlobalPackageReference Include="Microsoft.Build.CopyOnWrite" Version="1.0.0" />
</ItemGroup>
</Project>This example will include the Microsoft.Build.CopyOnWrite task for all NuGet-based projects in your repo.
If your project types don't support NuGet (e.g. .vcxproj), you can alternatively import this as an MSBuild SDK. In your Directory.Build.targets file:
<Project>
<Sdk Name="Microsoft.Build.CopyOnWrite" Version="1.0.0" />
<!-- ... -->
</Project>This SDK aims to improve the performance of large repositories by minimizing file copies during the build process. Many large repos have the snowball effect where Resolve Assembly Reference will add more and more dependencies that get copied along in different layers of the build graph. This is an attempt to accelerate those by taking advantage of the Copy on Write feature of the OS using this library: https://github.com/microsoft/CopyOnWrite.
Example build, internal Microsoft repo with 758 nodes, 3989 edges:
| Command | Value |
|---|---|
msbuild /p:EnableCopyOnWriteWin=false |
Time Elapsed 00:06:02.03 |
| Enlistment size | 66.4 GB (71,305,402,686 bytes) |
| Size on disk | 66.9 GB (71,848,480,768 bytes) |
| Command | Value |
|---|---|
msbuild /p:EnableCopyOnWriteWin=true |
Time Elapsed 00:04:09.32 |
| Enlistment size | 66.4 GB (71,305,402,686 bytes) |
| Size on disk | 3.83 GB (3,055,628,028 bytes) |
To use this feature, you need run on a drive formatted ReFS on Windows. This is only available on Windows Server, Enterprise, and Pro for Workstation SKUs.