[CentOS] Booting Software RAID

Tony Mountifield
Fri, 24 Jan 2014 17:08:28 -0000

In article <CAAOM8FXumoSAgbDe+PzryraRUHcsWOjWJQf-3Mc0TSn4ODRt9w at
mail.gmail.com>,
Matt <matt.mailinglists at gmail.com> wrote:
> I installed Centos 6.x 64 bit with the minimal ISO and used two disks
> in RAID 1 array.
>
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/md2         97G  918M   91G   1% /
> tmpfs            16G     0   16G   0% /dev/shm
> /dev/md1        485M   54M  407M  12% /boot
> /dev/md3        3.4T  198M  3.2T   1% /vz
>
> Personalities : [raid1]
> md1 : active raid1 sda1[0] sdb1[1]
>       511936 blocks super 1.0 [2/2] [UU]
> md3 : active raid1 sda4[0] sdb4[1]
>       3672901440 blocks super 1.1 [2/2] [UU]
>       bitmap: 0/28 pages [0KB], 65536KB chunk
> md2 : active raid1 sdb3[1] sda3[0]
>       102334336 blocks super 1.1 [2/2] [UU]
>       bitmap: 0/1 pages [0KB], 65536KB chunk
> md0 : active raid1 sdb2[1] sda2[0]
>       131006336 blocks super 1.1 [2/2] [UU]
>
> My question is if sda one fails will it still boot on sdb?  Did the
> install process write the boot sector on both disks or just sda?  How
> do I check and if its not on sdb how do I copy it there?

Tests I did some years ago indicated that the install process does not
write grub boot information onto sdb, only sda. This was on Fedora 3
or CentOS 4.

I don't know if it has changed since then, but I always put the following
in the %post section of my kickstart files:

# install grub on the second disk too
grub --batch <<EOF
device (hd0) /dev/sdb
root (hd0,0)
setup (hd0)
quit
EOF

Cheers
Tony
--
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org