Separate Jenkins config from build logs
If you're interested in only backing up configs, try installing the SCM Sync Configuration Plugin. This plugin syncs with a repo each time you change either a job or the Jenkins configs, but does not keep builds.

SCM Sync Configuration Jenkins/Hudson plugin is aimed at 2 main features :
Keep sync'ed your config.xml (and other ressources) jenkins/hudson files with a SCM repository
Track changes (and author) made on every file with commit messages

As a bonus you can set it to take a commit message each time you change a job, for easier restoration if necessary.