=====Change I/O scheduler=====
===Do you need to change the scheduler?===
CFQ is the default scheduler. If you have a specific use case, then you should benchmark the different schedulers.
Quote: [[https://www.kernel.org/doc/Documentation/block/cfq-iosched.txt]]
<code>CFQ has some optimizations for SSDs and if it detects a non-rotational
media which can support higher queue depth (multiple requests at in
flight at a time), then it cuts down on idling of individual queues and
all the queues move to sync-noidle tree and only tree idle remains. This
tree idling provides isolation with buffered write queues on async tree.</code>

===Current scheduler===
Check current scheduler setting for sda:<code>$ cat /sys/block/sda/queue/scheduler
[noop] deadline cfq</code>

===Change scheduler===
==Temporary==
  echo "noop" > /sys/block/sda/queue/scheduler

==For all disks==
Add to the kernel line in **/etc/grub.conf** <code>elevator=noop</code>

==For specific SSD's using udev==
Using udev:
<code>
/etc/udev/rules.d/60-schedulers.rules

# set noop scheduler for non-rotating disks
ACTION=="add|change", KERNEL=="sd[a-z]", TEST!="queue/rotational", ATTR{queue/scheduler}="noop"
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="noop"

# set cfq scheduler for rotating disks
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="cfq"
</code>