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vibe

WSL2 + btrfs

Inside WSL2, vibe runs as Linux and automatically picks the clone (cp --reflink) or rsync copy strategy — no configuration needed. But the WSL2 root filesystem is always ext4, which does not support reflink, so cp --reflink=auto silently falls back to a full copy.

To get real Copy-on-Write in WSL2, mount a separate btrfs volume and keep your project (e.g. node_modules) on it. Once the project lives on btrfs, vibe’s existing clone strategy produces instant CoW copies automatically.

Why the WSL root can’t do CoW

Section titled “Why the WSL root can’t do CoW”
  • The WSL2 root is ext4 and hardcoded — it is not configurable via .wslconfig or wsl.conf (ref microsoft/WSL#9339).
  • A “btrfs distro” (openSUSE / Fedora) does not help: WSL unpacks the rootfs into its own ext4 VHDX regardless.
  • Running btrfs-convert on the root is not viable — the converted root won’t boot in WSL.
  • reflink only works within the same filesystem, so the source and the copy must both live on the btrfs volume.

Recommended setup — mount a secondary btrfs VHD

Section titled “Recommended setup — mount a secondary btrfs VHD”

On the Windows side, in an Administrator PowerShell, create a VHD and attach it to WSL:

Terminal window
New-VHD -Path C:\wsl\dev-btrfs.vhdx -Dynamic -SizeBytes 128GB -BlockSizeBytes 1MB
wsl --mount --vhd C:\wsl\dev-btrfs.vhdx --bare

Then, inside WSL, format and mount the volume once:

Terminal window
lsblk                                  # find the new device, e.g. /dev/sdd
sudo mkfs.btrfs /dev/sdd
sudo mkdir -p /mnt/btrfs
sudo blkid /dev/sdd                    # copy the UUID
echo 'UUID=<uuid> /mnt/btrfs btrfs defaults,nofail 0 0' | sudo tee -a /etc/fstab
sudo mount -a
sudo chown $USER:$USER /mnt/btrfs


# Put the project on the btrfs volume; reflink works within it
mv ~/myproject /mnt/btrfs/myproject
cd /mnt/btrfs && cp --reflink=always -r myproject myproject-copy

Re-attach on reboot

Section titled “Re-attach on reboot”

wsl --mount --vhd ... --bare is a host-side operation and must be re-run after a Windows restart (for example, a Task Scheduler entry set to “Run with highest privileges” at login). Once the disk is attached, /etc/fstab mounts it automatically (automount.mountFsTab defaults to true).

Caveats

Section titled “Caveats”

References

Section titled “References”