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I Have a Schedule to Keep - IO Schedulers

The Linux kernel has several different IO schedulers. This article provides an introduction to the concept of schedulers and what options exist for Linux.

NOOP IO Scheduler
The NOOP IO scheduler is a fairly simple scheduler. With this scheduler all incoming IO requests are put into a simple First-In, First-Out (FIFO) queue and then executed. Note that this happens for all processes running on the system regardless of the IO request (read, write, lseek, etc.). It also does something called request merging. This is a feature that takes adjacent requests and merges them into a single request. This reduces seek time and improves throughput.

According to this article, the NOOP scheduler “… uses the minimal amount of CPU/instructions per I/O to accomplish the basic merging and sorting functionality to complete the I/O.” The IO scheduler assumes that some other device will optimize the IO performance. For example, an external RAID controller or a SAN controller could perform this optimization.

Potentially, the NOOP scheduler could work well with storage devices that don’t have…

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