[rrd-users] faking a datasource on the fly
linux at thehobsons.co.uk
Wed Jul 27 20:52:01 CEST 2011
Daniele Sluijters wrote:
>This one might sound familiar to some. MRTG has the (nasty)
>limitation that it needs to fetch pairs of data, it can't just fetch
>1 or 3 values, they must always be grouped in logical pairs.
>This presented a problem when 22.214.171.124.4.1.2021.4.13.0
>(ucdavis.memory.memShared) had to be fetched because that value
>isn't populated anymore. Instead however of returning 0 (which would
>be inaccurate) or Unknown (accurate) "Snmp no such object" is
>returned. This apparently confuses MRTG so much that even if the
>other OID which makes up the pair .126.96.36.199.4.1.2021.4.11.0 does
>respond with sane values an RRD is created with two datasource's
>which just always return NaN.
That's an MRTG issue, not an RRD issue. I'd suggest you should take
that up with the MRTG people.
For my uses, I use a script to fetch the data, apply any
manipulations required (for example, one of my sources returns an
integer which is 10x the real value so I have to add a decimal
place), and of course apply some sanity checks - one of which is "if
the value isn't available, use "U for the update".
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