[wincent]

The file system, the VCS, and the ability to index/grep the repo are just the tip of the iceberg. Pretty much everything that needs to access the filesystem or which depends on the contents/structure of the repo in some way needs to be re-built from scratch or otherwise dramatically customized to operate in this new landscape. That means a long catalog of tools and many years of effort.

This was already starting to become true even before FB switched to Eden, and before it switched to Mercurial (grepping, for example, was already back in the Git days being served by a custom grep service).