How to use the Noop or None IO Schedulers

Resolution

The noop scheduler is called none starting in RHEL 8.

Enable noop or none I/O scheduler

• Per device: (at runtime, lost once rebooted)
  • RHEL 8,9:[1] none scheduler option

    $ echo 'none' > /sys/block/sda/queue/scheduler
    $ cat           /sys/block/sda/queue/scheduler
    [none] mq-deadline kyber bfq 

  • RHEL 4,5,6,7:[1] noop scheduler option
    

    $ echo 'noop' > /sys/block/sda/queue/scheduler
    $ cat           /sys/block/sda/queue/scheduler
    [noop] anticipatory deadline cfq 

• All devices (at boot):
  • RHEL 7, 8: you can set none (RHEL 8) or noop (RHEL7) for all devices via editing /etc/default/grub as show below and then rebuilding the grub2 configuration file: (add option to existing GRUB_CMDLINE_LINUX line)

    Note: The elevator kernel parameter was marked for deprecation in RHEL8 and no longer has any effect from RHEL9 onwards.

    [root@host ~]# cat /etc/default/grub
    GRUB_TIMEOUT=5
    GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
    GRUB_DEFAULT=saved
    GRUB_DISABLE_SUBMENU=true
    GRUB_TERMINAL_OUTPUT="console"
    GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=rhel00/root rd.lvm.lv=rhel00/swap elevator=none"     <<= RHEL8 or later
    GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=rhel00/root rd.lvm.lv=rhel00/swap elevator=noop"     <<= RHEL7
    GRUB_DISABLE_RECOVERY="true"

  • Verify the /etc/default/grub file contains only one copy GRUB_CMDLINE_LINUX=
    

    # grep "GRUB_CMDLINE_LINUX" etc/default/grub | egrep -v "^#|GRUB_CMDLINE_LINUX_DEFAULT"1

  • Rebuild the /boot/grub2/grub.cfg file by running the grub2-mkconfig command as follows:
  • On BIOS-based machines:

    [root@host ~]# grub2-mkconfig -o /boot/grub2/grub.cfg 
    Generating grub configuration file ...
    Found linux image: /boot/vmlinuz-3.10.0-327.el7.x86_64
    Found initrd image: /boot/initramfs-3.10.0-327.el7.x86_64.img
    Found linux image: /boot/vmlinuz-0-rescue-537dacc8159a4d4caaa419342da0b820
    Found initrd image: /boot/initramfs-0-rescue-537dacc8159a4d4caaa419342da0b820.img
    done

  • On UEFI-based machines:
    

    [root@host ~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg 
    Generating grub configuration file ...
    Found linux image: /boot/vmlinuz-3.10.0-327.el7.x86_64
    Found initrd image: /boot/initramfs-3.10.0-327.el7.x86_64.img
    Found linux image: /boot/vmlinuz-0-rescue-537dacc8159a4d4caaa419342da0b820
    Found initrd image: /boot/initramfs-0-rescue-537dacc8159a4d4caaa419342da0b820.img
    done

  • RHEL 4, 5, 6: you can set noop for all devices via adding elevator=noop to the end of the kernel line in /etc/grub.conf file:
    

    title Red Hat Enterprise Linux Server (2.6.9-67.EL)
    root (hd0,0)
    kernel /vmlinuz-2.6.9-67.EL ro root=/dev/vg0/lv0 elevator=noop
    initrd /initrd-2.6.9-67.EL.img

 
tunables for none or noop IO schedulers
Individual IO scheduler personality tunables are located in /sys/block/sdN/queue./iosched. As seen below, the directory of tunables is empty - there are no tunables for the none (RHEL8,9) or noop (RHEL 4-7) IO schedulers.

• RHEL8,9:

  $ ls            /sys/block/sda/queue/iosched
  $

• RHEL 4,5,6,7:
  

  $ ls            /sys/block/sda/queue/iosched
  $

See Understanding the Noop IO Scheduler for further information.

noop vs none

The noop scheduler option within previous versions of RHEL is now called none with RHEL 8 and later versions. Although it has a new name, it still is same functions the same as RHEL 4-7's noop io scheduler.

• From RHEL 8's "Available disk schedulers", the none scheduler is describes as follows:

  none
  Implements a first-in first-out (FIFO) scheduling algorithm. It merges requests at the generic block layer through a simple last-hit cache.

• From RHEL 7's "I/O schedulers", the noop scheduler is described as follows:
  

  noop
  The noop I/O scheduler implements a simple FIFO (first-in first-out) scheduling algorithm. Requests are merged at the generic block layer through a simple last-hit cache. 

The two I/O schedulers perform the same function.

References

• Other means of automatically setting the I/O scheduler in a persistent manner across reboots:

  • "How to set a permanent I/O scheduler on one or more specific devices using udev"
  • "How to set a permanent I/O scheduler on one or more specific devices using tuned"

• RHEL 9:

  • "Monitoring and managing system status and performance"
    • "Chapter 9. Setting the disk scheduler"
      • "9.1. Available disk schedulers"

• RHEL 8:

  • "Managing storage devices"
    • "Chapter 17. Setting the disk scheduler"
      • "17.1. Available disk schedulers"

• RHEL 7:

  • "Performance Tuning Guide"
    • "Chapter 8. Storage and File Systems"
      • "8.1.1. I/O Schedulers", at the end of the section.