Physical disk performance
While a lot of high-level information about disk performance has been mentioned already, if you want to get useful benchmarks from drives you'll need to know a bit more about their physical characteristics. This will drop back to theory for a bit, followed by examples of real measured disks that demonstrate common things you can expect to see.
Random access and I/Os Per Second
Enterprise storage vendors like to talk in terms of Input/Outputs Per Second or IOPS. If you're buying a SAN for example, expect to be asked "how many IOPS do you expect in total and per spindle?" and for measurements provided by the vendor proving good performance to be in this unit. This number represents typical disk performance on a seek-heavy ...