To borrow a term from the Wikipedians: "Deletionist"

Unfortunately I don't remember.

As I recall, if you have a MacBook, iMessage syncs your messages and stores them in a file named ~/Library/Application Support/MobileSync/Backup

That file or files (my notes don't say number or the names of files) is just a SQL database which can be queried with the sqlite client, or exported into a more friendly format.

This solution worked for me about 5 years ago; I don't know if Apple still allows this.

More like the latter, except I use rsync (running over SSH) so as to minimize the amount of traffic. I understand syncthing works in a similar manner, but I haven't tried it out (I've heard good things about it though).

I have a very similar setup: an old PC with lots of big disk drives at my mom's house.

However, instead of leaving it powered on 24/7, I have it configured it to power itself on at a particular day and time every week. My backup script connects to it, mounts the disks, copies the data, and then send a shutdown command.

This way, the computer isn't running 24/7 (leaving it open to hacking attempts) , and the disks are only spinning when they're in use. It also saves my mom some money on her power bill :)

Just to be safe, I still have the PC plugged into a UPS.