Backup stalls server

I have a pretty extensive website that was easy to deploy (huge advantage of GetGrav). There is quite a bit of audio files I have tied into the site. I made the mistake of clicking the backup button, on the main screen. Apparently this does ALL my files! It takes a couple of hours to actually do full backup. The problem is, it brings my server to it’s knees. I’m on shared hosting, and all 5 of my websites become affected by this couple of hour slow down. So my real question is:

How do I stop the backup once I accidentally click the backup button?

It is more efficient for me to rsync my website to my desktop via ssh as my backup.