You have your answers, but I just want to note that what I do is run rsync from cron nightly, without the delete option.

Basically this reduces the chances of losing something by accidentally deleting it on the primary drive. Every few weeks/months, I run the rsync command with the delete option to clean up.

It's not a perfect backup by any means, especially since I could erroneously delete something right before that second rsync command and lose it for good. But it does provide a measure of safety.

There's also --delete-before which might help if your destination is tight on available space. And, as usual with 'traditional' tools, man-page is pretty good, there's a ton of parameters which might be helpful. And, as @hades@feddit.uk already mentioned, compression (-z) may actually hurt performance if you have a lot of bandwidth or if you're copying over already compressed data like JPGs.

-z might be pointless since you’re transferring files locally.

I do about the same, something like rsync -av --delete

I usually use rsync -azP --delete but I'm not sure if that's the best option.

Grsync makes this easier :)