Disable/Enable Readahead value for LVM volume with tuned running.

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 9

Issue

  • How to disable Readahead for LV with tuned service enabled?
  • How to set readahead value using custom systemd unit file with tuned enabled?

Resolution

  • Create a systemd service unit file, and make sure it starts after tuned service and set the needed value for read ahead in ExecStart:
# cat /etc/systemd/system/setra.service 
[Unit]
Description=Set custom read-ahead on LV
After=tuned.service
Requires=tuned.service

[Service]
Type=idle
ExecStart=/sbin/blockdev --setra 0 /dev/mapper/vgtest-lvtest

[Install]
WantedBy=multi-user.target
  • Enable the custom service:
#systemctl daemon-reload
#systemctl enable setra.service
  • Check the result:
# blockdev --report                 
RO    RA   SSZ   BSZ   StartSec            Size   Device
...
rw  8192   512  4096          0      2147483648   /dev/dm-0
rw  8192   512   512          0     18756927488   /dev/dm-1
rw     0   512   512          0      1073741824   /dev/dm-2   <-- 
rw  8192   512   512          0      2147483648   /dev/dm-3

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