The "ClusterStats Plugin" uses "Disk Usage" as its title.

<title>Disk Usage [Jenkins]</title>

There has been a pull request in GitHub since June 2013 that would fix this issue:
https://github.com/jenkinsci/cluster-stats/pull/1

Also, I find it a bit irritating that the plugin is called "ClusterStats Plugin" while the header on the page is "Jenkins Cluster Statistics". Maybe that could be changed to "ClusterStats" as well.