[arch-general] Why Is My RAID Installing Failing?

[Alexander Duscheleit]

On Tue, 12 Jan 2010 11:19:04 -0500
Carlos Williams <carloswill at gmail.com> wrote:

> Thanks for everyone's input. It appeared to have failed both ways. I
> guess Arch is not in the cards for me. It sucks because I love the
> rolling release aspect of Arch. I just find the documentation very
> confusing and something as simple as RAID should be far more
> simplistic even for a text based installer. Hopefully developers are
> looking into improving this in future releases.

I didn't know, where to put a proper reply in this thread, because
basically you are all doing the same mistake. I will just outline the
procedure here briefly and then explain where it all went wrong :)

1 - cfdisk  # the settings in Carlos' 1st mail look sane
2 - modprobe raid1
3 - mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda2 /dev/sdb2 
4 - /arch/setup # we save the mdadm -D --scan for later
!!!! 5 - before getting to the "Configure System" part,
         open up another console (Alt-F2) and do
         mdadm -D --scan >> /mnt/etc/mdadm.conf
         (you have to do this before mkinitcpio runs
         in the "Configure" stage, but after the target
         system is mounted, so between "Install Packages"
         and "Configure System" should be fine)
6 - continue the setup as described in OP (skip the cp -a part)


Now to why you have to do it this way:
the file /etc/mdadm.conf tells mdadm where the proper disks/partitions are
to find to build it's arrays. Therefore the mdadm hook adds this file
to the initrd together with the mdadm binary. The mdadm call during init
will then use this file, assemble your arrays and then hand of the boot
process to the "real" system.

All your tries with the "new methos" thus just failed, because you copied
/etc/mdadm.conf too late, and it was never added to the initrd file. Mdadm
inside the ramfs just never knew what to look for.

You also have to remember later, to regenerate mdadm.conf and your initrd 
everytime you change major parts of your RAID setup.

I hope this helps to clear some things up.

Greetings,
	jinks
(running mdraid with the "new method" on at least five boxes atm :))