[gentoo-user] How to build a time machine on Gentoo

[Nganon]

Hello all,

My first post on the list. I thought I would start with something that I
started
to think of as 'essential' after losing 90GB of data. Now I have two main
questions in mind: what to and how to back up on gentoo most efficiently.

1. Apart from users' home directories and the followings, what should be
backed
up on a gentoo machine?
/etc/portage/
/root
/var/lib/portage
...?

2. Erm..okay, I am gonna say, what magic I want and then ask your way.
I first started making gzipped tar balls as follows:

tar czpf /media/backups/userA-`date +%Y.%m.%d`.tgz -X userA-excludelist /etc

But these can get huge especially for home dirs. I also want safe dvd
copies.
Though I can find enough space on the external drives, I don't trust them
any more. See above..sigh..(No I recovered about one third of it with
testdisk/photorec
which names them as file000001 file00002.. and half them are zero sized..
which
quite justifies my agony)

Here is what I wanna do. I want to have only one big backup for, say,
userA-2010.08.07.tgz and other small backup tars containing only the
files/folders that were modified since last update, 2010.08.07, as
userA-diff-2010.08.14.tgz, userA-diff-2010.08.21.tgz,
 userA-diff-2010.08.28.tgz
etc. Now if I want to take the userA back to the future, 2010.08.21,  I want
to
do it by first extracting the huge tar userA-2010.08.07.tgz and then the
tiny
backup userA-diff-2010-08-21.tgz.

But the thing is I don't know how to do this. I am hoping maybe you can tell
me
how to of it as well as a better way of doing backups.

By the way, since I want dvd backups as well, and I want to use +rw dvds so
I
can overwrite old backup after a while, what is best way of ensuring the
integrity and safety of them. Is it a good idea to use truecrypt containers?
Or
nothing tops signing and encrypting with gpg?

Thanks for any comment in advance.