For rhel 6  see tuned and tuned-adm

View the sheduler used to write to disk.

cat /sys/block/sda/queue/scheduler


Set the scheduler to write directly to io device without delay. 
should do that for SAN 

echo noop > /sys/block/sda/queue/scheduler


To have it persistent at reboot add the following to grub.conf

elevator=noop


When testing for performance don't forget to clear the cache first

cat /proc/sys/vm/drop_caches
free
sync
echo 3 > /proc/sys/vm/drop_caches
free