Input/output (I/O) scheduling is the method that computer operating systems use to decide in which order I/O operations will be submitted to storage volumes. I/O scheduling is sometimes called disk scheduling.
The position of I/O schedulers within various layers of the Linux kernel's storage stack.
I/O scheduling usually has to work with hard disk drives that have long access times for requests placed far away from the current position of the disk head (this operation is called a seek). To minimize the effect this has on system performance, most I/O schedulers implement a variant of the elevator algorithm that reorders the incoming randomly ordered requests so the associated data would be accessed with minimal arm/head movement.
I/O schedulers can have many purposes depending on the goals; common purposes include the following