Hi,
TL;DR version:
A few customers will see new bandwidth graphs appearing in their
Cacti, which can be found at
https://tools.bitfolk.com/cacti/
The already-existing graphs will continue to run for a while and
then will cease to be updated. The new graph will become your
primary bandwidth graph.
This is because some high-bandwidth users need to have graphs based
on 64-bit counters, not 32-bit, in order to accurately measure
bandwidth use.
It may result in slightly higher values being reported in Cacti, but
this is merely correcting previous under-reporting. Monthly totals
as presented in our emailed data transfer reports were/are correct.
Longer version:
While investigating some recent discrepancies between the different
systems we have for accounting for customer data transfer, I
discovered that all of our bandwidth graphs were using 32-bit SNMP
counters.
A 32-bit unsigned counter has a maximum value of 4,294,967,295. With
5 minute sampling, that means that an interface seeing around
114Megabit/sec of traffic will reach 4,294,967,295 and wrap around
to zero again before the counter can be read.
As a result, a few customers who routinely use large amounts of
bandwidth have Cacti graphs that are under-reporting their usage.
Here is an example of a graph based on 32-bit counters:
http://tools.bitfolk.com/cacti/graph_5062.html
Here is the same interface graphed from 64-bit counters:
http://tools.bitfolk.com/cacti/graph_5617.html
You can see that the first daily graph has several drop-outs around
high bandwidth periods, and that the total data transferred in the
last 24 hours is under-reported in the first daily graphs.
I will not go through and replace every bandwidth graph with new
ones, only those of customers who are seen to be transferring more
than ~4.2GB in 5 minutes. So if you see a new graph appearing, this
is why.
Measuring 32-bit counters on a 2x 1 gigabit interface was of course
a very silly oversight, and it is now apparent that even the virtual
network device in an individual VPS has no problem exceeding
~114Mbit/s.
Cheers,
Andy
--
http://bitfolk.com/ -- No-nonsense VPS hosting
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