[mrtg] Re: Legends

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Wed Dec 19 01:46:48 MET 2001

Herms, Mark wrote:
> I'm trying a test on my system to monitor the hard drive. It's a Dell
> Optiplex GX240 with a 40GB disk, one partition. I'm not sure if the
> MaxBytes: is correct. I get a graph that the YLegend goes up to 4000.0 k and
> the short Legend displays this:
> Max Usage 3747.4 kGB (0.1%) Average Usage 3747.4 kGB (0.1%) Current Usage
> 3747.4 kGB (0.1%) 

This is of course wrong.  kGB, would it exist, would mean kilogigabyte
which would mean you have 3,747,400,000,000,000 bytes free...

This means 3.7 Petabytes of free space.  That would allow quite a lot
of super-high quality movies :)

(kilo == 1000, mega == 1000 kilo, giga == 1000 mega, tera == 1000 giga,
peta == 1000 tera  -->  peta == 1000*1000*1000*1000*1000).

Step 1: determine what numbers you collect.  Are they bytes, kilobytes,
        kibibytes (see http://physics.nist.gov/cuu/Units/binary.html)
        or something else. Also determine *what* you measure.  Is it
        free space or used space ?
Step 2: determine how to let MRTG know about this unit.  See, amongst
        other sources, the faq.mrtg.org page, FAQ section, configuring.

> Could someone help me with what the legends should say. And if the MaxBytes
> is correct?

It seems to me that you are monitoring free space and that you are
getting units of kilobytes (or more likely: kibibytes).

If you leave out the GB you'd have 3.747400 megabytes free which
could be right. I think it is more likely that you have used
3747.4*1024*1000 = 3837337600 bytes which MS would probably show as
being 3659 MB.  That would mean you have about 36,1 GB free space.

Some random tips:

Make sure the numbers don't reach 2**31 = 2147483648.  This means
you can't work with bytes so multiplying by 1000 will not work.

You can graph MBs by dividing the number you get from SNMP by 1000
(or, assuming kibibytes: 1024).

To let MRTG know you don't feed it bytes you need to use the kMG option
(this is in the faq).

> MaxBytes[Local_DSK_C]: 4000000000
This is 4 gigabyte, not 40.

> ShortLegend[Local_DSK_C] : GB

Never (or at least: almost never) use a prefix here.  This means B
in stead of GB.  MRTG will almost always put a prefix here, this is
why you see a double prefix (kGB).  Using the kMG modifier you'd get
something like 

> Legend1[Local_DSK_C]:
> Legend2[Local_DSK_C]: Disk Space Available in GBytes

Make sure you get "available" in stead of "used".

> LegendO[Local_DSK_C]:  Usage

You should use "Free" here, or "Used" in the normal legend.

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
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