Installing grub bootblocks
With multi-disk mirrors as system disks, you need to make sure every disk in the mirror can boot the system if necessary. With a normal install, only the first disk will probably end up with bootblocks, which makes you sad if that disk fails and you have to boot off one of the other members of the mirror.
If root mirror is on /dev/sda and /dev/sdl for example:
grub --no-floppy > device (hd0) /dev/sda > root (hd0,0) > setup (hd0)
Then repeat for the rest of the disks with:
device (hd0) /dev/sdl