Copy-on-write fuse filesystem
to check out a whole group of repositories without using more disk space
http://m.cacm.acm.org/magazines/2016/7/204032-why-google-stores-billions-of-lines-of-code-in-a-single-repository/fulltext "Most developers access Piper through a system called Clients in the Cloud, or CitC, which consists of a cloud-based storage backend and a Linux-only FUSE13 file system. Developers see their workspaces as directories in the file system, including their changes overlaid on top of the full Piper repository. CitC supports code browsing and normal Unix tools with no need to clone or sync state locally. Developers can browse and edit files anywhere across the Piper repository, and only modified files are stored in their workspace. This structure means CitC workspaces typically consume only a small amount of storage (an average workspace has fewer than 10 files) while presenting a seamless view of the entire Piper codebase to the developer."
I talked to a friend working at Google this week-end, and he had me dreaming with this feature :) Especially because in our case we use NFS, which makes everything unbearably slow.
Microsoft made this https://news.ycombinator.com/item?id=13559662#13560550
Appears to be Windows-specific though :(