Gathering statistics on disk usage

Dan Nelson dnelson at allantgroup.com
Sat Oct 15 09:36:22 PDT 2005


In the last episode (Oct 15), Josh Paetzel said:
> I am trying to set up mrtg to graph disk usage.  I've tried using the
> output of iostat to provide me with usage in MB/s.  The problem with
> this is that moving data from disk to disk on the system causes the
> usage to jump to around 30MB/s.  Even with mrtg configured to draw
> the graphs logarithmically they basically blow up and the normal
> transfers are not really visable.  systat -vm gives statistics on
> disk usage with a percent busy field.  This stat would be easier to
> graph and I would like to use it.  My problem is that I can't seem to
> extract the output of systat properly.  I've tried doing systat -vm |
> tail -n -1 and that doesn't work.  I've also tried systat -vm >
> somefile.txt and that doesn't work.  There doesn't seem to be a way
> to get systat to run once and then quit either.
> 
> Can anyone think of a way to either capture systat's output or
> recommend a utility that will give me a % busy output?  I've tried
> iostat without success.

If you apply the patch at
http://www.freebsd.org/cgi/query-pr.cgi?pr=bin/68840, you will be able
to get %busy stats out of iostat.

You can also try installing net-snmp and polling the diskIOLA5 value
for the disk, but on my system at least, the values don't seem to make
sense (I have seen numbers from -2546 to 3000).

-- 
	Dan Nelson
	dnelson at allantgroup.com


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