I'm using the community version of OpsCenter to monitor my clutster. At the moment I'm interested in storage space. In the performance metrics page, if I choose to see the graph of a the metric "CF: SSTable Size" for a certain CF of interest,  two things are plotted on the graph: Total disk used (Total) and Live disk used (Total). Does anyone know what they mean? And what is the difference? "Total disk used" gives me the same value as the size on disk of the files corresponding to the CF in the data directory (all files starting with CF name and having Statistics, Data, Filter, Index or Compacted). But what is the "Live disk used"? I thought it is just the raw data on disk (column names and values) without any SSTable overhead, but this is not true because it reports a lower value than if I see the disk usage of just the "CFName-..-Data.db" files.
 I'm always confused about what all the metrics in the OpsCenter mean and how they are calculated. Is there a reference explaining all of them? Most are mapped to the JMX attributes exposed...but even for those, I've never found a reference explaining them in detail. Any suggestions?


P.S.  I'm using Cassandra 0.8.5