Copy-on-Write in Win32 API Early Access
On October 25, 2023, the Windows filesystem team released an early preview of copy-on-write (CoW) linking in the Windows 11 Insider Canary channel. This builds automatic CoW linking into the Win32
CopyFile APIs when using Dev Drive or ReFS. If released next year, this will eliminate the need to update build engines, tools, and runtime frameworks to support CoW. Related release information is here.
We released some early benchmarks showing the automatic gain for .NET
File.Copy() without the need for explicitly updating tools to use CoW. In testing a large C# repo under this new configuration, we saw a 32% reduction in build time just moving to Dev Drive, then CoW linking increased that win to 42%.
If you have builds or other workloads that do a lot of copying, join a machine to the Canary Insider release and run benchmarks on a Dev Drive to discover the gains you can achieve.