In my setup, I have two disks that are each formatted in the following way: (GPT)1)  1MB   BIOS_BOOT2)  300MB LINUX_RAID   3)  *     LINUX_RAID   The boot partitions are mapped in /dev/md0, the rootfs in /dev/md1. md0 is formatted with ext2, md1 with XFS. (I understand that formatting has to be done on the md devices and not on sd - please tell me if this is wrong). How do I setup GRUB correctly so that if one drive fails, the other will still boot? And by extension, that a replacement drive will automatically include GRUB, too? If this is even possible, of course. 
How to correctly install GRUB on a soft RAID 1?
linux;grub2;software raid;xfs
If the two disks are /dev/sda and /dev/sdb, run both grub-install /dev/sda and grub-install /dev/sdb. Then both drives will be able to boot alone.Make sure that your Grub configuration doesn't hard-code disks like (hd0), but instead searches for the boot and root filesystems' UUIDs.I'm not aware of support in Grub to declare two disks as being in a RAID-1 array so that grub-install would automatically write to both. This means you'll need to run grub-install again if you replace one disk; it's one more thing to do in addition to adding new members to the RAID arrays.