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sources/tech/20160104 How to Change Linux IO Scheduler.md

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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:
+
+1. noop – is often the best choice for memory-backed block devices
+2. cfq – A fairness-oriented scheduler. It tries to maintain system-wide fairness of I/O bandwidth.
+3. Deadline – A latency-oriented I/O scheduler. Each I/O request has got a deadline assigned.
+4. 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
+```
+
+--------------------------------------------------------------------------------
+
+via: http://linuxroutes.com/change-io-scheduler-linux/
+
+作者：[UX  Techno][a]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]:http://linuxroutes.com/change-io-scheduler-linux/