Subversion backup/ha solution

I have a subversion server (centos 5) with about 50 users. Everything is working fine, but I'm thinking about make sure I will not lost everthing if hardware failure happen. After some quick research, almost every question about Subversion ha solution point me to http://www.wandisco.com. But it's not a open source software. So I want to ask redditor about your Subversion backup/ha strategy.

Any advice is appreciated, thanks.