Set the disk scheduler using TuneD

You can create and enable a TuneD profile that sets a given disk scheduler for selected block devices. The setting persists across system reboots.

Before you begin

About this task

When creating a TuneD profile to set a disk scheduler, replace:

  • device with the name of the block device, for example sdf and
  • selected-scheduler with the disk scheduler that you want to set for the device, for example bfq.

Procedure

  1. Optional: Select an existing TuneD profile on which your profile will be based. For a list of available profiles, see TuneD profiles distributed with RHEL.
  2. To see which profile is currently active, use: 
    # tuned-adm active
  3. Create a new directory to hold your TuneD profile: 
    # mkdir /etc/tuned/profiles/<new_profile>
  4. Find the system unique identifier of the selected block device: 
    # udevadm info --query=property --name=/dev/device | grep -E '(WWN|SERIAL)'
     
    ID_WWN=0x5002538d00000000_
ID_SERIAL=Generic-_SD_MMC_20120501030900000-0:0
ID_SERIAL_SHORT=20120501030900000
    Note
    This command returns all values identified as a World Wide Name (WWN) or serial number associated with the specified block device. Although using a WWN is preferred, it is not always available for every device. In such cases, you can use any value returned by the example command as the device system’s unique ID.
  5. Create the /etc/tuned/profiles/<new_profile>/tuned.conf configuration file. In the file, set the following options:
    1. Optional: Include an existing profile: 
      [main]
include=<existing-profile>
    2. Set the selected disk scheduler for the device that matches the WWN identifier: 
      [disk]
devices_udev_regex=IDNAME=device system unique id
elevator=selected-scheduler

      Here:

      • Replace IDNAME with the name of the identifier being used (for example, ID_WWN).
      • Replace device system unique id with the value of the chosen identifier (for example, 0x5002538d00000000). To match multiple devices in the devices_udev_regex option, enclose the identifiers in parentheses and separate them with vertical bars: 
        devices_udev_regex=(ID_WWN=0x5002538d00000000)|(ID_WWN=0x1234567800000000)
  6. Enable your profile: 
    # tuned-adm profile <new_profile>

Results

  1. Verify that the TuneD profile is active and applied: 
    $ tuned-adm active
     
    Current active profile: <profile>
     
    $ tuned-adm verify
     
    Verification succeeded, current system settings match the preset profile.
See TuneD log file ('/var/log/tuned/tuned.log') for details.
  2. Read the contents of the /sys/block/device/queue/scheduler file: 
    $ cat /sys/block/device/queue/scheduler
     
    [mq-deadline] kyber bfq none

    In the file name, replace device with the block device name, for example sdc. The active scheduler is listed in square brackets ([]).