This scheduler implements request merging, a one-way elevator, read and write request batching, and attempts some anticipatory reads by holding off a bit after a read batch if it thinks a user is going to ask for more data.
This is optimised for the single disk systems.
The scheduler implements request merging, a one-way elevator, and imposes a deadline on all operations to prevent resource starvation.
Complete Fair Queueing Scheduler (CFQ)
The scheduler implements both request merging and the elevator, and attempts to give all users of a particular device the same number of IO requests over a particular time interval.