Rootless fuse-overlayfs performance on different filesystems?

[saolof]

Fuse-overlayfs will try to use reflinks to copy files up when available: https://github.com/containers/fuse-overlayfs/blob/main/main.c#L3261

I assume that this means that performance may be better when ran on top of xfs and btrfs as opposed to running it on ext4 when layers are merged?

[nalind]

It should make "copy ups" faster when writing to content that's supplied by a read-only layer in an overlay mount.

[saolof]

Cool, does that happen during image builds and creation of overlays from images as well?

[nalind]

It's not something that happens when the contents of layers are being placed on disk, i.e., when pulling images or starting containers, when using the overlay driver. It comes into play when something in a container's rootfs is modified, which can happen when running a container or handling a RUN instruction during a build.