It is not a secret that while processors, memories and peripherals have constantly increased their speed (sometime in a more then linear manner), the commons storage subsystems where constantly lagging behind the other components.
This is hardly a surprise, considering that the great majority of the commons permanent data storage systems are based on mechanical (rather than electronic) devices. This mechanical nature intrinsically mean that these devices are way slower than processors and other electronic devices. For example, consider the probably most common storage media: the hard disks. While these devices have grown in capacity and offer an outstanding space/cost ratio (today you can buy an high-quality 2 TB disk for less than 200€, while 10 years ago you had to pay about the same money for a 20 GB disk) their speed evolved with a much, much lower rate. This is indeed due to the fact that these mechanical devices have two moving parts: the rotating platters (activated by an electric motor) and the heads (moved around by an actuator).
So, while high capacity guarantee you high sequential read and write speed (because the platter's areal density was improved tremendously over time), random read and write speed are only a little fractions of the maximum theoretical speed and are only a little better than those of a 10 years old disk. At the same time these moving parts also imply that hard disk are prone to fault with an order of magnitude (or more) greater that other pure electronic parts.