[CentOS] CentOS 7 install on one RAID 1 [not-so-SOLVED]

Wed Jan 25 16:46:26 UTC 2017
Tony Mountifield <tony at softins.co.uk>

In article <1485342377.3072.6.camel at biggs.org.uk>,
Pete Biggs <pete at biggs.org.uk> wrote:
> On Tue, 2017-01-24 at 17:14 -0500, m.roth at 5-cent.us wrote:
> > So, it installed happily.
> > 
> > Then wouldn't boot. No problem, I'll bring it up with pxe, then chroot and
> > grub2-install.
> > 
> > Um, nope. I edited the device map from hd0 and hd1 being the RAID to
> > /dev/sda and /dev/sdb, then ran grup2-install. It now tells me can't
> > identify the filesystem on hd0, and can't perform a safety check, and
> > gives up.
> > 
> > What am I missing? Google is not giving me any answers....
> > 
> Surely, if you are using software RAID, then you should configure that
> RAID in anaconda, that will then cope with setting up the partitions to
> allow booting.  Basically it needs a small non-RAID partition to hold
> /boot on the boot disk.
> Remember that the boot sequence is generally: BIOS reads MBR and
> executes it; MBR code reads kernel from /boot and executes it (yes,
> it's more complicated than that). If the MBR code doesn't know how to
> read a RAID partition, then it's going to fail, that's why you have a
> small non-RAID partition to hold /boot.
> Hardware RAID is different because it interfaces at the BIOS level so
> the MBR code doesn't need to know how to specifically read it.

If you are using RAID 1 kernel mirroring, you can do that with /boot too,
and Grub finds the kernel just fine. I've done it many times:

1. Primary partition 1 type FD, size 200M. /dev/sda1 and /dev/sdb1.
2. Create /dev/md0 as RAID 1 from /dev/sda1 and /dev/sdb1.
3. Assign /dev/md0 to /boot, ext3 format (presumably ext4 would work too?)
4. Make sure to setup both drives separately in grub.

Typically I then go on to have /dev/sda2+/dev/sdb2 => /dev/md1 => swap,
and /dev/sda3+/dev/sdb3 => /dev/md2 => /

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