HBase should expose via JMX how much HDFS disk space it is using. See http://search-hadoop.com/m/s9VIx4Hhjz .
Moving out of 0.94.1
Removing from 0.94. Otis, please let me know if you want to be pulled into a future 0.94 release.
Moving this nice-to-have metric that probably better belongs in hdfs out of 0.96. Move it back if I called it wrong.