Periodically backup SVN server is a good practice. It's also useful when you want to relocate your svn server. Here are the simple steps:

1. login to the svn server

2. backup your svn repo, if more then one repo, do it one by one

svnadmin dump /path/to/reponame > /path/to/reponame.svndump

3. You can also compress the backup

svnadmin dump /path/to/reponame | gzip > reponame.svndump.gz

4. To unzip the backup

gunzip reponame.svndump.gz