Mailing the story:

Storage performance has failed to keep up with that of other major components of computer systems. Hard disks have gotten larger, but their speed has not kept pace with the relative speed improvements in RAM and CPU technology. The potential for your hard drive to be your system's performance bottleneck makes knowing how fast your disks and filesystems are and getting quantitative measurements on any improvements you can make to the disk subsystem important. One way to make disk access faster is to use more disks in combination, as in a RAID-5 configuration.