Storage of data in Cassandra

Certain values, like ifHighSpeed, are stored in when using RRD.
Where and how are those values stored when using Cassandra.

This questions stems from the following problem:
On April 06, an interface’s ifHCOutOctets value should have triggered a threshold violation (MIB2 group - interface surpassing 90% of bandwidth). It did not. Given the expression:
ifHCOutOctets * 8 / 1000000 / ifHighSpeed * 100
and having check the values (graphically) of ifHCOctets, the only thing I can REACH for is that ifHighSpeed violated the resource filter constraint
and so the trigger did not fire

I created a graph to “view the value” of ifHighSpeed during the period in question and it is at an acceptable value (100). HOWEVER, it occurred to me that ifHighSpeed might still be stored ala and that which is currently displayed is somehow not updated collected value.