UnionFS came out of the my advisor's first phd students new lab (stoneybrook). Aufs itself was inspired by that. My inspiration came from saying we should combine this semantic with linux package management semantics (as can be seen clearly from the papers where I give a summary of it).

I took unionfs and modified to be more dynamic. i.e. for persistent containers, enable layers to be marked unlink and replaced with different layers (they would remain part of the union for data operations, but would be invisible to file system name oriented operations, ex: lookup()/readdir()). Idea for this was to enable a container to upgrade itself if the template it was based on was upgraded. I wasn't thinking what became the cattle/pet metaphor, was focused on creating a system that would work equally well for persistent and ephemeral containers.