Neither is using macfuse as a stand in for overlayfs and bind mounts.

My point is "as fast as it gets" is using MacOS how MacOS is designed: ie, through sandboxing and not containerization that pretends the MacOS userspace is Linux. It's not Linux.

There is a fundamental trade off between isolation and performance. You cannot securely share resources without overhead.

FUSE is only used for bind mounts. If you write to a directory that belongs to container, you get the raw speed of host OS.

How do you support layers without overlayfs?

It's not me, it's containerd "native" snapshotter. It turns to be efficient on macOS thanks to `clonefile` syscall.