[justinlloyd]

Have been running ReFS on a drive on my Windows 10 workstation for about three years, and recently started using a dev drive equivalent on Windows 10 for the past two months. Our Unreal Engine project is quite large, 600+GB straight from the P4 depot before building. I need to keep a few separate workspaces around, one for current development work, one for swarm reviews, one for "let me test out a thing that might break" because as we know, branching in Perforce can quite painful, especially on large depots. At one point I needed to have dozens of workspaces synced to specific changelists whilst we hunted down a bug in one of our levels.

ReFS, with block de-duplication and LZ4 compression has reduced the per-workspace footprint to around 10% of what it was previously. Decreased build times by around 5% and decreased archive, stage and package times by about 80% by deploying MSBuild SDK CopyOnWrite. I also moved the DDC onto the VHDX where the project resides which has further reduced the footprint of the project.

Windows 11 canary channel (still in canary I think) has a modified Win32 that supports CoW FileCopyEx. You can get similar gains by other means on Win10 and Win11 by using ReFS CoW aware utilities.

Have used XFS, BTRFS, APFS and others extensively over the years, so I am glad that Windows is finally getting in on the action.