orachk -Linux Disk I/O Scheduler should be configured to Deadline
1.cat /etc/grub.conf,have set "elevator=deadline"
device (hd0) HD(1,800,64000,c4745fa4-8015-47c0-abde-30be20f5e1ea)
default=0
timeout=5
splashimage=(hd0,1)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux (2.6.32-431.el6.x86_64)
root (hd0,1)
kernel /vmlinuz-2.6.32-431.el6.x86_64 ro root=UUID=431e6461-5682-4e30-9a33-4e76b6505671 elevator=deadline rd_NO_LUKS rd_NO_LVM LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet hugepages=4100 transparent_hugepage=never
initrd /initramfs-2.6.32-431.el6.x86_64.img
2.cat /sys/block/sda/queue/scheduler