Changing default IO scheduler linux

Change default Linux IO scheduler to optimize IOs (very important if server is VM)

Check existing (active) io scheduler (elevator):

[root@server ~]# cat /sys/block/sda/queue/scheduler

noop anticipatory deadline [cfq] # cfq active

Change it on the fly

[root@server ~]# echo noop > /sys/block/sda/queue/scheduler

or

[root@server ~]# echo deadline > /sys/block/sda/queue/scheduler

Change it permanently = append elevator=deadline to grub.cfg kernel line, reboot

title CentOS
root (hd0,0)
kernel /vmlinuz-2.6.32-279.19.1.el6.x86_64 ro root=/dev/mapper/vg-lv_root …   ….  elevator=deadline

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