How do websites (like government ones) store passwords long term?

So how do websites keep passwords long term? I mean really important websites, say a government one.

Sure, they store a hash (or salted hash) of the password in the webserver-connected datastore that is used for authentication, but is that it?

In fact, how do websites like Facebook store passwords? I'm guessing they would have multiple copies of the hash spread out over the world? And backed up to tape once in a while?