calculating available disk space

Hello,

I'm trying to use the "disk" directive in snmpd.conf to monitor available
diskspace.

I'm a little confused though at how it goes about calculating the percentages.

For example:

I have the line "disk / 95%" in snmpd.conf (the number is very high to make it
easy for the event to trigger).

Using dd, I've been creating files to fill up the harddrive to try and work
out at what point net-snmp sees the available space fall below 95%. The
problem is that dskErrorFlag isn't being set until the available space falls
to approx 90%.

I can see why it's happening, but I don't quite understand why.

I think the free percentage is being calculated by doing percentAvail = 100 -
(dskUsed/dskTotal) * 100

Doing it this way gives you a completely different result to doing
percentAvail = dskAvail/dskUsed * 100

This is because the values for dskAvail + dskUsed != dskTotal

The data below shows how much I had to fill the harddrive before the errorflag
tripped to on - it didn't trip until the free space was down to 90% (as
calculated by avail/total).

Is this the intended behaviour or is there something weird going on? For the
time being I've sent disk to trip at an absolute Kb value, but I would prefer
it to work on percentages.

dskEntry.dskTotal.1 = INTEGER: 74975192
dskEntry.dskAvail.1 = INTEGER: 67771760
dskEntry.dskUsed.1 = INTEGER: 3394824
dskEntry.dskPercent.1 = INTEGER: 5
dskEntry.dskPercentNode.1 = INTEGER: 0
dskEntry.dskErrorFlag.1 = INTEGER: 1

I hope this makes sense...

Helen.


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