Gathering statistics on disk usage

[Josh Paetzel]

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.
 
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Thanks,

Josh Paetzel