[mrtg] Re: unknaszero

[George Chelidze]

Cliff wrote:
> Hi George,
> 
> Saturday, March 22, 2003, 2:16:49 AM, you wrote:
> 
> GC> (Verstrooid) Profke wrote:
> 
>>>>1. If the data didn't come, then graph updates with 0 value
>>>>2. On some devices, interface table contains interface entry only if 
>>>>interface is up, in this case, graph doesn't update because mrtg 
>>>>received data indicating there is no data in MIB with appropriate OID
>>>>
>>>>How do you folks think, is this correct? I'd like mrtg updates it's 
>>>>graphs in both cases.
>>>>
>>>
>>>Updates will be made the moment the interface comes up again.
>>
> 
> GC> I know, but do you think this is correct? I think it shoult update it 
> GC> all the time with zero value.
> 
>  Depends what one is graphing.

It depends only for choosing "should I use unknaszero option?". If I 
decided to use it (that means I understand that in case of unknown data, 
it's possible to graph "incorrect" data, but it's ok in my case and I 
want it to work exectly this way), it should do it's work

> 
>  In the case of disks:
>  If for some reason, mrtg can't get it's numbers...
>  Is it more likely to be close to it's last known value
>  or is it more likely that the disk contained no data?

Sure It's more likely that it's close to last number, but according to 
definition of unknaszero (zero if data is _unknown_), I should get zero 
instead of waiting when data become available and then draw zero anyway.

>  In the case of leased lines that are up almost all the time:
>  Is it more likely that the leased line was actually down or
>  was it more likely that the line was carrying some traffic ?
>  
>  And is the point of the graphs to show actual downtime?
>  
>  Or is the graph used for capacity planning, where one wants
>  to know what the averages and peaks are over the average month?
>  So it depends.
> 
> 
> 

Once again:

definition_0:
unknaszero - Log unknown data as zero instead of the default behaviour 
of repeating the last value seen. Be careful with this, often a flat 
line in the graph is much more obvious than a line at 0.

definition_1: (from faq.html)
The problem is that MRTG doesn't know *why* the data didn't come back, 
all it knows is that it didn't come back. It has to do something, and it 
assumes it's a stray lost packet rather than an outage.

fact_0:
when some interface is down, interface data isn't available and nas 
returns error "noSuchName", Options include "unknaszero", graphs do not 
update until interface is still up.

The data is unknown at least in two cases:

1. data didn't came back
2. nas returned "noSuchName"

according to definition_0 in both cases 0 should be graphed. fact_0 
shows the different action.

Best Regards,
-- 
George Chelidze



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