In many database situations, what you're also concerned about is the streaming sequential read or write rate of the drive, where it's just staying in one area instead of seeking around. Computing this value is complicated by the nature of how disks are built.
The first thing to realize about modern hard disks is that the speed you'll see from them depends highly on what part of the disk you're reading from. Disks spin at one speed all of the time, referred to as constant angular velocity (CAV). A typical drive nowadays will spin at 7,200 RPM, and the actual disk platter is circular. When the disk read/write head is near the outside of the disk, the speed of the part passing underneath it is faster than on the inside. ...
