docker use linux kernel almost as native, so performance is well.
in mac or windows, things are different. there is no linux kernel.
so some helper needed.
docker-machine: a tool to install docker in virtual machine. Dockerized hosts (hosts with Docker Engine on them).
docker for Mac/Windows: even still run a virtual machine (super hidden ).with its own hypervisor “hyperkit” and shared file system “osxfs”. Unfortunately, “osxfs” wasn’t very fast.
but in many cases, realtime host-virtual consistence is not necessary.
So options come
host first docker run -v hostDir1:/virtualDir1:cached
virtual first docker run -v hostDir1:/virtualDir1:delegated
realTime run -v hostDir1:/virtualDir1:consistent