Google has a very vast herd of machines with a
large number of hard drives. Very fruitful
that they analyze failures and publish
the results to the web!
While the drives they are studying are definitely
not classic (all dating from 2001 or later),
those of us who host large quantities of classic
material may find the results of interest:
http://labs.google.com/papers/disk_failures.pdf
Side note: at one point I found it unbelievable
that Google was using consumer-grade hardware
to host their stuff. Since then, I've developed a
lot of respect for this approach!
Tim.