Disk I/O Statistics not displaying graph

Disk I/O Statistics not displaying graph

Monitoring disk I/O statistics of a RedHat Linux host and the graphs do not display.  I get a message from the AppManager "There is no data available at the moment", however, AppManager is polling device I/O information.  What must be done to display I/O statistic graph, and be able to pull up I/O trending data over a period of time?

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