it seems that boot system (and many other things) on centos6 changed a little bit.
Since today when I want to move disks from one server to another it was enough to boot the centos system in rescue, chroot, update kernel (to rebuild initrd needed for software raid and other modules), reinstall grub on boot partitions and voila all was fine.
Now Centos6 have a new feature called “dracut” which does not agree with the above solution (just throw a kernel panic ’cause no root disk found, no raid started), so all you need to do is rebuild initrd (initramfs file) using dracut command line:
mv /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.old
dracut –mdadmconf –force /boot/initramfs-$(uname -r).img $(uname -r)
important thing is to set the same name from /boot/initramfs-xxx.img here and in grub.conf and set the next parameter to the kernel version you will use after (if you have just boot in rescue).
After that system will boot just fine.