CentOS - Mar 2015 - RAID1 bootloader configuration on CentOS 6.x and 7

Hi,

The CentOS wiki sports a page about setting up software RAID1 on CentOS 
5.x. There's a section about making both members of the RAID1 bootable 
by setting up GRUB on both disks.

Now I wonder how this should be done on CentOS 6.x and 7. I have two 
sandbox machines in my office, one running a minimal CentOS 6.6, the 
other one with a CentOS 7 installation.

Correct me if I'm wrong, but I guess the setup on CentOS 6.6 is similar 
to the one described on the wiki page for CentOS 5.x, something like:

grub> device (hd0) /dev/sda
grub> device (hd1) /dev/sdb
grub> root (hd0,0)
grub> setup (hd0)
grub> root (hd1,0)
grub> setup (hd1)
grub> quit

Now how would that work with the new GRUB2 under CentOS 7? Or maybe it's 
already installed on both disks, but how would I know that?

Cheers,

Niki
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On Sun, Mar 29, 2015 at 3:43 AM, Niki Kovacs <info at microlinux.fr>
wrote:
> Now how would that work with the new GRUB2 under CentOS 7? Or maybe
it's
> already installed on both disks, but how would I know that?
grep grub2-install /path/to/anaconda/logs/program.log

I forget if it accepts two devices on a line, or if it takes separate
commands. But

grub2-install /dev/sdX
grub2-install /dev/sdY

That will work on BIOS.

On UEFI this is totally fakaked right now as neither GRUB upstream nor
distros have a proper user friendly solution for this at all. CentOS
7's installer offers an improper user friendly solution which allows
you to RAID 1 the EFI System partitions with md raid.

On UEFI, I do a post-install alteration to make it something more
standard with the way upstream ought to be doing it. That means two
grub.cfg's: a generic one on the ESPs that merely forwards to
/boot/grub2/grub.cfg. That makes the ESP contents generic and never
modified again. And then the real grub.cfg is /boot/grub2/grub.cfg
which can of course then be on raid1 or raid 5 or whatever, and this
is the file that gets updated when there are kernel updates.


-- 
Chris Murphy