OS: Tuning Completely Fair Queueing CFQ I/O scheduler
The Completely Fair Queueing (CFQ) I/O scheduler controls the way the Linux kernel commits reads and writes to disks and works to optimize disk access times.
Without an I/O scheduler, the kernel would issue each request in the order that it is received, resulting in thrashing: if one process reads from one part of the disk, and one writes to another, the heads would have to seek back and forth across the disk for every operation. You can use the CFQ scheduler to control how the kernel reads and writes to disks to avoid thrashing. Note: Using other schedulers with the SAP SD workload in the test environment did not result in a performance gain. Ensure that CFQ is the I/O scheduler enabled on your system with the following command:
# cat /sys/block/<device>/queue/scheduler # noop anticipatory deadline [cfq]
where device is the name of the disk on which you want CFQ to run.
The brackets ([]) indicate the scheduler that is currently in effect. Or, you can change the assigned scheduler with the following command:
# echo cfq > /sys/block/<device>/queue/scheduler
where device is the name of the disk on which you want to change the assigned scheduler.