If the load on a server keeps on increasing and noticed that caused by  raid process then,

Check  /proc/mdstat

#cat /proc/mdstat

Personalities : [linear] [raid0] [raid1]
md0 : active raid1 sda4[0] sdb4[1]
482359552 blocks [2/2] [UU]
resync = 58.7% (283626752/482359552) finish=376.7min speed=8789K/sec

If you see some thing like this . There may be some rebuilding going

resync = 58.7% (283626752/482359552) finish=376.7min speed=8789K/sec

we can see the speed here . That is causing the load . Make that speed around 1000

cd /sys/block/md0/md

cat sync_speed_max

8789 (system)

reduce the speed by issuing the command

echo 1000 > sync_speed_max

This will make server stable.