Local mirror of which server? Your own?
You can do it a number of ways. If just a backup, you could rsync everything in terms of configuration for DNS, squid, Apache, samba. I don't see a reason for doing a backup of the squid cache, as it expires anyway. With rsync, you can use it just to pick up changes, and also with the --delete parameter, it will delete and user data that was deleted between backups. Otherwise, it will just keep adding and adding files even if a user deleted.
Rsync can be done over SSH, or you can setup rsyncd on the server in question, and then just make a cron to run nightly.
Alternatively, if you want to mirror it, you could also have it run as an active/standby server with HA. If one fails, then the other becomes active without having to restore data from a backup. It all depends on what exactly you want to achieve.