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How to Change Linux I/O Scheduler
Linux I/O Scheduler is a process of accessing the block I/O from storage volumes. I/O scheduling is sometimes called disk scheduling. Linux I/O scheduler works by managing a block device’s request queue. It selects the order of requests in the queue and at what time each request is sent to the block device. Linux I/O Scheduler manages the request queue with the goal of reducing seeks, which results in great extent for global throughput.
There are following I/O Scheduler present on Linux:
- noop – is often the best choice for memory-backed block devices
- cfq – A fairness-oriented scheduler. It tries to maintain system-wide fairness of I/O bandwidth.
- Deadline – A latency-oriented I/O scheduler. Each I/O request has got a deadline assigned.
- Anticipatory – conceptually similar to deadline, but with more heuristics to improve performance.
To View Current Disk scheduler:
# cat /sys/block/<Disk_Name>/queue/scheduler
Let’s assume that , disk name is /dev/sdc, type:
# cat /sys/block/sdc/queue/scheduler
noop anticipatory deadline [cfq]
To change Linux I/O Scheduler For A Hard Disk:
To set a specific scheduler, simply type below command:
# echo {SCHEDULER-NAME} > /sys/block/<Disk_Name>/queue/scheduler
For example,to set noop scheduler, enter:
# echo noop > /sys/block/sdc/queue/scheduler
The above change is valid till reboot of the server , to make this change permanent across reboot follow below procedure:
Implement permanent setting by adding “elevator=noop” to the default para in the /boot/grub/menu.lst file
1. Create backup of menu.lst file
cp -p /boot/grub/menu.lst /boot/grub/menu.lst-backup
2. Update /boot/grub/menu.lst
Now add “elevator=noop” at the end of the line as below:
Example
kernel /vmlinuz-2.6.16.60-0.91.1-smp root=/dev/sysvg/root splash=silent splash=off showopts elevator=noop