git.kernel.org mirror at Google

This is not possible for us, for a number of reasons.

The backend storage is not the standard Git filesystem format. A client that rsync copied our data would have some Git-looking stuff, but it may be also appear to be corrupt. This is because we sort of use the Git file formats, but we have modified them slightly to work around some limitations in our storage system. We patch up the format on the fly to be Git standard when speaking with a client using the Git protocol. Doing that same patch up work with rsync would be difficult.

The other reason this won't work is our network only routes HTTP. We can't route rsync from the client into the backend server that is handling the request.

> It would also be good to know if rsync or git is used
> to keep up this mirror

The mirror uses git://git.kernel.org/ to fetch repositories. It has a complete list of the available repositories, and polls each one with git fetch every 30 minutes. Because we use git to update the mirror, the mirror is always "Git consistent", it never exposes transient corruption to a client. This is unlike git.kernel.org, which uses rsync to update itself, and can fail client requests because of remote corruption where rsync didn't get everything in a single pass.