In Linux, the I/O scheduler is a kernel component that manages the I/O requests for a block device, such as a hard disk. There are several different I/O schedulers available in Linux, and you can choose which one to use for a particular hard disk.
To change the I/O scheduler for a hard disk in Linux, you can use the echo command to write to the /sys/block/DEVICE/queue/scheduler file, where DEVICE is the name of the block device. For example, to change the I/O scheduler for the sda hard disk to the deadline scheduler, you can use the following command:
echo deadline > /sys/block/sda/queue/scheduler
This will change the I/O scheduler for the sda hard disk to the deadline scheduler.
You can use the cat command to view the available I/O schedulers for a particular hard disk. For example:
cat /sys/block/sda/queue/scheduler
This will display a list of the available I/O schedulers for the sda hard disk, with the current scheduler enclosed in square brackets.
To make the change permanent, you will need to edit the /etc/rc.local file and add the echo command to set the I/O scheduler at system startup. Open the /etc/rc.local file with a text editor, such as vi or nano, and add the echo command before the exit 0 line. Save the changes to the file and exit the text editor.