Linked from: Configuring Partitions and RAID
We are almost done with the software RAID configuration. Next, the installation wizard will ask for the boot loader settings.
If the secondary disk fails (/dev/sdc), then the system will still be bootable. If the primary disk fails (/dev/sda), then your system will not boot. In order to make the secondary disk bootable as well, run the following command:
grub-install /dev/sdc