CFQ [cfq] (Completely Fair Queuing) is an I/O scheduler for the Linux kernel and default under many Linux distributions.

Noop scheduler (noop) is the simplest I/O scheduler for the Linux kernel based upon FIFO queue concept.

Anticipatory scheduler (anticipatory) is an algorithm for scheduling hard disk input/output as well as old scheduler which is replaced by CFQ

Deadline scheduler (deadline) - it attempt to guarantee a start service time for a request.

First, make sure NOOP is an option for you. The following command will show you the scheduler being used. Substitute your own block device for “sda.”

$ cat /sys/block/sda/queue/scheduler
noop anticipatory deadline [cfq]

The one in brackets is the active scheduler. To switch to NOOP, add “elevator=noop” to the default kernel parameters in /etc/grub.conf. Something like:

title Red Hat Enterprise Linux Server (2.6.32-431.el6.x86_64)
   root (hd0,0)
   kernel /vmlinuz-2.6.32-431.el6.x86_64 ro root=/dev/mapper/Volume00-root rd_NO_LUKS LANG=en_US rd_NO_MD SYSFonT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=Volume00/root selinux=1 audit=1 KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet elevator=noop
   initrd /initramfs-2.6.32-431.el6.x86_64.img

Reboot and rerun the test above, the brackets should move to noop.

Sample output:

noop anticipatory deadline [cfq]

Task: Set I/O Scheduler For A Hard Disk

To set a specific scheduler, simply type the command as follows:
# echo {SCHEDULER-NAME} > /sys/block/{DEVICE-NAME}/queue/scheduler
For example, set noop scheduler, enter:
# echo noop > /sys/block/hda/queue/scheduler