On Mon, Apr 13, 2015 at 07:29:18PM -0400, Nico Kadel-Garcia wrote:
> > I am not sure what you refer to. With SL5 and SL6 you have 2 disks,
> > put "/" on a software RAID1 partitions put grub on both disks ...
>
> Until it fails. Grubby, along with the kernel installlation RPM,
> doesn't know how to update, manage, or keep synchronized this second
> /boot partition. Hilarity can then ensue, along with making sure that
> your /etc/fstab doesn't detect the wrong disk and mount it incorrectly
> as /dev/sda. See, if your first disk dies, unless you're very cautious
> with /etc/fstab, it's very much a crapshoot if hte right partition
> will mount as "/boot".
> 
> Been there, done that, gave up on the silliness.
> 

You talk about /boot, /dev/sda, grubby, etc, I doubt you have been there, done that. Gave up, sure.

With mirrored disks, there is only /dev/md0 ("/"), /dev/md1 (swap), etc (if you have /home, /data, etc),
in /etc/fstab, "/" is mounted by UUID of the /dev/md0 RAID1 device,
which in turn is assembled by UUID of component disks using mdadm magic.

grubby is not used. (in fact, the SL6.6 installer installs the correct grub
magic on both component disks of raid1 "/" on /dev/md0).

there is no /etc/fstab mounting the "wrong disk" "as /dev/sda". In fstab
are instructions to mount "/" by UUID which happens to be the UUID of /dev/md0,
which in turn is assembled by mdadm, also by UUID, there is no possibility
of mounting "the wrong disk".

If one of the disks fails, all that happens is /dev/md0 is assembled as a degraded raid1 array,
there is no data loss.

Hmm... forgot to mention one piece of magic - bootable raid1 arrays have to have
superblock version 0.9 or 1.0. Versions 1.1 and 1.2 are not bootable. Again
the SL6 installed automatically creates the correct superblock version 1.0
for "/" on a raid1 array.

-- 
Konstantin Olchanski
Data Acquisition Systems: The Bytes Must Flow!
Email: olchansk-at-triumf-dot-ca
Snail mail: 4004 Wesbrook Mall, TRIUMF, Vancouver, B.C., V6T 2A3, Canada