They wrote something that allowed them to virtualize Git -- can't remember the name of that. But it basically hydrated files on-demand when accessed in the filesystem.

The problem was I think something to do with like the number of git objects that it was scaling to causing crazy server load or something. I don't remember the technical details, but definitely something involving the scale of git objects.

I thought Microsoft made a number of improvements to git to allow it work with all of their internal repos.