Abstract: I/O scheduling of video server is discussed.Throughthe optimization of the motion of disk arm and the rotation latency,we get the Bi-SCAN scheduling algorithm.For heterogeneous system,which is required to support multi-rate videos, we put forward CDL and CTL scheduling schemes based on Bi-SCAN.And conditions of admission control of theses schemes are offered.Simulations are performed to test the performance of them.At last an improved CDL scheduling scheme is proposed which is based on bucket control.

Key words: video server, I/O scheduling algorithm, CDL, CTL, leaky bucket