[gentoo-user] {OT} backups... still backups....

[Grant]

Remote, automated, secure backups is the most difficult and
time-consuming Gentoo project I've undertaken.

Right now I'm pushing data from each of my systems to a backup server
via rdiff-backup.  The main problem with this is if a system is
compromised its backup is also vulnerable.  Also, you can't restrict
rdiff-backup to a particular directory in authorized_keys like you can
with rsync, and rdiff-backup isn't very good over the internet (I've
had trouble on sub-optimal connections) and it's recommended on the
mailing list to use rdiff-backup either before or after rsync'ing over
the internet.

We've discussed this vulnerability here before and it was suggested
that I use hard links to version the rdiff-backup repository on the
backup server in case it's tampered with.  I've been studying hard
links, cp -al, rsnapshot (which uses rsync and hard links), and rsync
--link-dest (which uses hard links) but I can't figure out how that
would work without the inevitable duplication of data on a large
scale.

Can anyone think of an automated method that remotely and securely
backs up data from one system to another, preserves permissions and
ownership, and keeps the backups safe even if the backed-up system is
compromised?

I did delve into bacula but decided it was overkill for just a few systems.

- Grant