If it's a docker problem maybe you're running it with the vfs storage driver which copies every layer every time instead of using overlayfs? If not then it may be a problem with the virtualization solution, not docker itself. VM overhead shouldn't be 5x, not even for IO. Unless you're trying to mount parts of the host filesystem, that's slow with pretty much any virtualization solution, perhaps barring virtio-fs, but that's probably not supports on osx