Second copy of LUKS header

Issue 77 by ryan.castellu... on 2010-08-14 00:38:30:

It would be really nice if cryptsetup could keep a second copy of the LUKS header at the END of the container. Should probably be an optional thing but on by default. One concern with this would be older versions of cryptsetup not updating the second copy when the first is changed - eg the key-slot you thought you flushed is still there. Not sure what a good way to deal with that would be.