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Bootable raid1 on UEFI

From: Chris Murphy
Subject: Bootable raid1 on UEFI
Date: Sun, 2 Feb 2014 12:47:33 -0700

Simple case on BIOS: two disks that we want to boot linux from reliably even in 
the face of a one disk failure. 

Therefore /boot is on an md raid1 device. All of the md raid1 member disks have 
sufficient MBR gap for grub-install to be executed on each disk. Only one 
grub.cfg is needed at /boot/grub and as that single file is updated, it's 
mirrored on all member disks. It's very straight forward with existing 
grub-install and grub-mkconfig tools.

However, it's not so straightforward on UEFI with Secure Boot. I can manually 
create an ESP on each member disk, and copy signed grubx64.efi to each ESP, and 
place a grub.cfg [1] on each ESP that forwards to the "real" 
/boot/grub/grub.cfg on the md device. But how does upstream intend this to be 
done with existing tools? 

Chris Murphy


# forward to real config
          search --no-floppy --fs-uuid --set=root --hint-bios=hd$d,gpt2 
--hint-efi=hd$d,gpt2 --hint-baremetal=ahci$d,gpt2  
          configfile /boot/grub2/grub.cfg

$d is for each disk so that the hint is only looking for the fs-uuid on the 
local disk first. The /boot/grub2/grub.cfg is on md raid1 (it could also be 
raid10, or raid5 or Btrfs raid1, 10 so there are many other use cases.) 
Alternatively the ESPs each have a "real" grub.cfg, both of which need to be 
updated any time there's a kernel update, which is a problem because only one 
ESP is mounted at /boot/efi.

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