System update spec proposal

[Christopher Blizzard]

A note about the history of using rsync.  We used rsync as the basis for
a lot of the Stateless Linux work that we did a few years ago.  That
approach (although using LVM snapshots instead of CoW snapshots)
basically did exactly what you've proposed here.  And we used to kill
servers all the time with only a handful of clients.  Other people
report that it's easy to take out other servers using rsync.  It's
pretty fragile and it doesn't scale well to entire filesystem updates.
That's just based on our experience of building systems like what you're
suggesting here and how we got to where we are today.

--Chris