There are 2 ways that I know of to do this, for real time, click on the interface in webfig and open it up, scroll to the bottom and you should have both a real time byte graph and a real time packet graph.
For non-volatile samples, set up graphing (webfig->tools-graphing) add all interfaces. Can be accesses from the interface graph on that page or best from webfig-> graphing (will pop a new window with a menu for all available graphs). Since the sample time defaults to 5 minutes it will take a while to populate.
Hope this helps!
JT
PS: And of course you can always set up MRTG and monitor all interfaces remotely via SMNP.
you could enable snmp and use a third party site for monitoring ex www.odmon.com
it gives you a more granular graphic Hourly (1 Minute Average), Daily (5 Minute Average), Weekly (30 Minute Average), Monthly (2 Hour Average) and Yearly (1 Day Average)
i use this site because i don’t want to write graphic data to the nand flash, and if i get power failures then the information is lost.
If you want some free solution, then design your own using Linux base MRTG, but it do requires Manual handwork, or more suitably it should be called artwork