John,
> This would imply that an upgrade in drive RPM should be accompanied by
> a decrease in random_page_cost, correct?
Maybe. Maybe not. Tom's Hardware did some Bonnie++ testing with a variety
of new drives last year. They were moderately surprised to find that there
were "faster" drives (i.e. higher RPM) which had lower real throughput due to
poor onboard software and hardware, such as a small and slow onboard cache.
So, it would be reasonable to assume that a 10,000 RPM Barracuda could support
marginally lower random_page_cost than a 7,200 RPM Barracuda ... but that
tells you nothing about a 10,000 RPM Maxtor Diamond (as an example).
Also, many other factors influence real random_page_cost; the size and access
pattern of your database is probably much more important than your RPM.
--
-Josh Berkus
Aglio Database Solutions
San Francisco