Prologue: sda old but works, sdc defective. I will replace sdc.
First of all, mark disk sdc as defective and remove from raid.
mdadm --manage /dev/md0 --fail /dev/sdc2 mdadm --manage /dev/md1 --fail /dev/sdc1 mdadm --manage /dev/md2 --fail /dev/sdc3 mdadm /dev/md0 -r /dev/sdc2 mdadm /dev/md1 -r /dev/sdc1 mdadm /dev/md2 -r /dev/sdc3
Physically replace disk and copy partition table to new one.
sfdisk -d /dev/sda | sfdisk /dev/sdc OR you may try sfdisk /dev/sda > sda_parttable_mbr.bak sfdisk /dev/sdc < sda_parttable_mbr.bak
Add new partitions to raid
mdadm /dev/md0 -a /dev/sdc2 mdadm /dev/md1 -a /dev/sdc1 mdadm /dev/md2 -a /dev/sdc3
Install grub (grub 1.x on CentOS6, so enter “grub” in shell and then
device (hd0) /dev/sdc root (hd0,1) setup (hd0)