I originally posted this at http://bdgregg.blogspot.com/2005/11/sys-admin-magazine-december-2005-copy.html.
The December, 2005 copy contains an article on the DTraceToolkit written by Ryan Matteson. Grab a copy! The article is "Observing I/O Behavior with the DTraceToolkit", and is quite good. It was also selected as the feature article – which means it will be available online for some time:
Thanks Matty, and Sys Admin Magazine!