Oracle Tips by Burleson

Disk I/O Tuning

Chapter 1: General Disk Architecture

The rotational latency is related to the speed at which the disk rotates. There is also the positional latency which is mostly determined by how fast the disk actuator can move. These combined latencies form the basis for the seek times for the drives. Seek times generally determine how fast data can be retrieved from a specific disk.

With a magnetic drive the read/write head(s) float over the disk surface on the long actuator arm. Sudden physical shocks can cause the actuator arm to flex causing the read-write heads to momentarily make contact with the disk surface. The effects of the read-write heads coming in contact with the surface of a disk vary from little damage and no loss of data to a severe disk crash with loss of all data unless sophisticated and expensive disk recovery processes are used. I have seen disk failures (head crashes) where the magnetic media was gouged off down to the aluminum substrate.