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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/

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如何更改IO调度器
==================================
Linux IO 调度器，IO调度器也叫磁盘调度器。Linux IO调度器的机制主要是控制块设备的请求队列：确定队列中哪些IO的优先级更高以及何时下发IO，以此来减少磁盘寻道时间，从而提高系统的吞吐量。
目前Linux上有如下几种IO调度算法：
1. noop - 通常用于内存存储的设备.
2. cfq - 绝对公平调度器. 进程平均使用IO带宽.
3. Deadline - 每一个IO，都有一个最晚执行时间.
4. Anticipatory - 启发式调度，类似Deadline算法，但是引入预测机制提高性能.
查看设备当前的IO调度器：
```
# cat /sys/block/<Disk_Name>/queue/scheduler
```
假设磁盘名称是 /dev/sdc:
```
# cat /sys/block/sdc/queue/scheduler
noop anticipatory deadline [cfq]
```
### 如何改变硬盘设备I/O调度器
使用如下指令：
```
# echo {SCHEDULER-NAME} > /sys/block/<Disk_Name>/queue/scheduler
```
比如设置 noop 调度器:
```
# echo noop > /sys/block/sdc/queue/scheduler
```
以上设置重启后会失效，要想重启后配置仍生效，需要在内核启动参数中将 "elevator=noop" 写入 /boot/grub/menu.lst:
#### 1. 备份 menu.lst 文件
```
cp -p /boot/grub/menu.lst /boot/grub/menu.lst-backup
```
#### 2. 更新 /boot/grub/menu.lst
将 "elevator=noop" 添加到文件末尾，比如:
```
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：[honpey](https://github.com/honpey)
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/