Re: raid startup on a live CD?

[NeilBrown <neilb@suse.de>]

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Could you try again, but add --verbose to --incremental --scan,
report the output, and any message that appear in 'dmesg'.

thanks,
NeilBrown



On Mon, 14 Nov 2011 22:56:40 -0600 Hank Barta <hbarta@gmail.com> wrote:

> Hi folks,
> On occasion I boot a live CD and need to have the md RAID devices
> running. Ordinarily (with Ubuntu live CDs) I find that I need to
> install the mdadm package after booting the live CD. At that point my
> recollection is that the RAID devices get started by the scripts that
> perform the installation (and probably run the startup scripts that
> are in /etc/init.d/...)
> 
> Earlier today I did this with a distro that is derived from Debian and
> under development. I was happy to see that 'mdadm' was already
> installed. (I had asked for this in fact.) But then I started
> encountering difficulties. The /proc/mdstat file existed but listed no
> RAID personalities and none of my devices were started. I tried 'mdadm
> --assemble -scan' which reported no errors but did not improve the
> situation. I manually loaded the raid0 and raid1 modules (which caused
> the personalities to be listed in /prod/mdstat) and pulled in other
> raid related kernel modules. However 'mdadm --assemble -scan' still
> did not start my devices. I thrashed around a bit before finding a
> command that probed drives and listed the md devices and their UUIDs.
> I was then able to start them using 'mdadm --assemble /dev/md<n>
> --uuid <UUID>' individually for the RAID devices I wanted to start.
> 
> I'd like to report back to the person working on this distro the
> difficulties I had with the RAID and beyond that, I'd like to provide
> the information that they need to set up RAID so it just works (like
> on a normal boot) if possible and desirable.
> 
> First... Are there reasons that other live CDs I've used have not set
> up RAID? Live CDs by their nature are somewhat lightweight so if
> adding mdadm uses significant resources perhaps it is best left as a
> manual operation.
> 
> Is there something I overlooked in getting it started in this
> particular situation?
> 
> Where should I be looking for documentation that would help
> configuring RAID on a Live CD? I did some searching and the most
> promising thing I found was
> https://raid.wiki.kernel.org/articles/r/a/i/RAID_Boot_bac9.html which
> directs me to a text file in the kernel source tree.
> (http://lxr.linux.no/#linux+v3.1.1/Documentation/filesystems/ramfs-rootfs-initramfs.txt)
> And that points to other documentation. I'd appreciate pointers to
> documentation that is particularly relevant to md RAID form a live CD.
> 
> many thanks,
> hank
> 
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