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

[Alexander Duscheleit]

On Tue, 12 Jan 2010 20:49:40 -0500
Baho Utot <baho-utot at columbus.rr.com> wrote:

> [...]
> >
> > 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.
> >
> 
> Only if you use the madam hook,  I use just the raid and encryption
> hook and it works for me.
> 
> I am using raid5 with encrypted root and home filesystems (on the
> Arch install) , everything is encrypted except /boot ( it is not
> mounted  into the filesystem and is not in fstab )

Yes, I was mostly implying use of the mdadm hook. I personally don't
like overly long boot lines in grub. I have no idea why the "raid" hook
also failed for others, I haven't used it in a long time.

> [...]
> 
> Let me suggest you have a look at the raid howto on slackware12.2 or
> 13.0 dvd.
> 
> ftp://carroll.cac.psu.edu/pub/linux/distributions/slackware/slackware-13.0/README_RAID.TXT
> 
> Slack uses lilo but if you define the array on the kernel line in
> grub it works just the same.
> 
> /boot/grub/menu.lst
> 
> timeout 5
> default 41
> color green/black light-green/blue
> 
> title ArchLinux x86_64
> root (hd0,1)
> kernel /vmlinuz26 cryptdevice=/dev/md2:root root=/dev/mapper/root 
> md=2,/dev/sda5,/dev/sdb5,/dev/sdc5 ro
> initrd /kernel26.img
AFAIK the md=2,... line is read by the 'raid' hook to assemble the
raids via mdadm command line.
> 
> title Slackware 12.2-x86
> root (hd0,1)
> kernel /Slackware/vmlinuz root=/dev/md2
> md2=,/dev/sda5,/dev/sdb5,/dev/sdc5
> 
> Notice no initrd in the above
I'm not entirely sure, *how* the system manages to find raid-members
and assembles them in this cases.
A while ago there was a kernel-level raid auto detection which is
marked as deprecated and advised against in favor of userspace raid
assembly via initrd.
Perhaps Slackware is still using this feature. It didn't work for me
either on gentoo or arch though.
This would indicate, that the md=2,... line is superfluous in this case.
> 
> Here is /etc/mdadm.conf from Slack and the Arch install has an empty
> file for /etc/mdadm.conf.
> 
> Please read the second paragraph, closely read the functioning of
> madm without a configuration file.
> 
> # mdadm configuration file
> #
> # mdadm will function properly without the use of a configuration
> file, # but this file is useful for keeping track of arrays and
> member disks. # In general, a mdadm.conf file is created, and
> updated, after arrays # are created. This is the opposite behavior
> of /etc/raidtab which is # created prior to array construction.
> [...]

My guess is "function properly" here means working with already
detected/assembled arrays.
Mdadm doesn't seem to try and autodetect arrays it doesn't know about
yet.

Greetings,
	jinks