IO Scheduler

Introduction

The Linux kernel, the core of the operating system, is responsible for controlling disk access by using kernel IO scheduling.

This article explains how-to change the IO scheduler without recompiling the kernel and without restart.

Check the currently used IO scheduler

cat /sys/block/sda/queue/scheduler

noop anticipatory [deadline] cfq

Proxmox VE uses deadline by default, delivers best performance on hardware raid and SAN environments.

Switching IO Schedulers on runtime

Set the scheduler for /dev/sda to Deadline:

echo deadline > /sys/block/sda/queue/scheduler

Set the scheduler for /dev/sda to CFQ:

echo cfq > /sys/block/sda/queue/scheduler

Set IO Schedulers permanently

In order to choose a new default scheduler you need to add the following into your /etc/default/grub:

nano /etc/default/grub

GRUB_CMDLINE_LINUX_DEFAULT="... elevator=deadline"

or:

GRUB_CMDLINE_LINUX_DEFAULT="... elevator=cfq"

After you change /etc/default/grub you need to run update-grub to apply changes:

update-grub

Links

• http://en.wikipedia.org/wiki/Deadline_scheduler
• http://en.wikipedia.org/wiki/CFQ