I produced some nice looking graphs of my hard drive speed using iozone, a 
free opensource disk io benchmarking utility at http://www.iozone.org/.

The graphs can be found at
http://morning.ecet.vtc.edu/~jlaughli/powermac/
I should have noted on the graph that all sizes are in kilobytes, while 
speed measurement is in kilobits per second.

For both read and write operations, it is clear to see how the disk cache 
helps speed up transfers up until the size of the transfers exceed the size 
of the disk cache, and then the speed is bottlenecked by the actual speed 
of the scsi bus.

The read graph has a couple of "interesting" features, though. Note the 
holes that occur around 8 & 16k files with 1k record sizes, and the less 
prominent holes at 2k record sizes with 32 and 512k files, and also a 
smaller hole at 8k files x 4k records. Can these be explained? They are not 
present in the re-read graph, which shows a much more uniform slope.

The write graph isn't all that interesting, all though that little notch 
and that little hole intrigue me. I probably should have used a different 
scale to show more detail, but I wanted to use the same scale as on the 
other tests.

The re-write graph is perhaps the most interesting of all. What the heck is 
going on there? I should really run the tests 10 times or so and average 
the results, it's possible cron decided it was going to execute a job or 
something just then.

I would like to display the graphs with a finer resolution in the Z axis, 
perhaps even a continuous gradient. I can't quite figure out how to get 
excel to do something like that though. If anyone has tips for that, they'd 
be appreciated.

-Jeff