[CentOS] Looking for a RAID1 box

Fri Jan 6 16:45:41 UTC 2023
Chris Adams <linux at cmadams.net>

Once upon a time, Simon Matter <simon.matter at invoca.ch> said:
> Are you sure that's still true? I've done it that way in the past but it
> seems at least with EL8 you can put /boot/efi on md raid1 with metadata
> format 1.0. That way the EFI firmware will see it as two independent FAT
> filesystems. Only thing you have to be sure is that nothing ever writes to
> these filesystems when Linux is not running, otherwise your /boot/efi md
> raid will become corrupt.
> Can someone who has this running confirm that it works?

Yes, that's even how RHEL/Fedora set it up currently I believe.  But
like you say, it only works as long as there's no other OS on the system
and the UEFI firmware itself is never used to change anything on the FS.
It's not entirely clear that most UEFI firmwares would handle a drive
failure correctly either (since it's outside the scope of UEFI), so IIRC
there's been some consideration in Fedora of dropping this support.

And... I'm not sure if GRUB2 handles RAID 1 /boot fully correctly, for
things where it writes to the FS (grubenv updates for "savedefault" for
example).  But, there's other issues with GRUB2's FS handling anyway, so
this case is probably far down the list.

I think that having RAID 1 for /boot and/or /boot/efi can be helpful
(and I've set it up, definitely not saying "don't do that"), but has to
be handled with care and possibly (probably?) would need manual
intervention to get booting again after a drive failure or replacement.

Chris Adams <linux at cmadams.net>