Prevent Autodetection

Prevent Autodetection

[Richard Laager]

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I have a virtualization host running on an MD root filesystem. I also
have two whole disks allocated to a virtualized guest which is doing an
MD RAID1. The host is seeing the array (i.e. it shows up
in /proc/mdstat). I'd like to prevent this, if for no other reason than
if there's a problem with that array, it prevents (or at least delays)
booting the host.

I've tried setting "AUTO +1.x homehost -all" "AUTO homehost -all" and
even "AUTO -all" in /etc/mdadm/mdadm.conf. I'm updating the initrd and
rebooting after each change. I've tried "msdos" as well as GPT labels on
the disks used by the guest. In every case I've tried, it's still
imported.

I'm running Ubuntu 12.04 "Precise" on both the host and the guest.

$ uname -a
Linux HOSTNAME 3.2.0-45-generic #70-Ubuntu SMP Wed May 29 20:12:06 UTC
2013 x86_64 x86_64 x86_64 GNU/Linux

$ mdadm --version
mdadm - v3.2.5 - 18th May 2012

Does this suggest the initrd scripts are broken on Ubuntu, am I doing
something wrong, or is it just not possible to prevent this
autodetection?

Thanks for any insight you can provide!

-- 
Richard

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Re: Prevent Autodetection

[Richard Laager]

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On Tue, 2013-06-11 at 03:18 -0700, Jeff Johnson wrote:
> Did you try changing the disk partition types from 'fd' (Linux MD
> autodetect) to something like '83' (Linux)?

I did not with the msdos partition table, but I performed the equivalent
with GPT ("set 2 raid off" in parted).

-- 
Richard

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Re: Prevent Autodetection

[Dmitrijs Ledkovs]

Hello,

On 11 June 2013 10:36, Richard Laager <rlaager@wiktel.com> wrote:
> I have a virtualization host running on an MD root filesystem. I also
> have two whole disks allocated to a virtualized guest which is doing an
> MD RAID1. The host is seeing the array (i.e. it shows up
> in /proc/mdstat). I'd like to prevent this, if for no other reason than
> if there's a problem with that array, it prevents (or at least delays)
> booting the host.
>
> I've tried setting "AUTO +1.x homehost -all" "AUTO homehost -all" and
> even "AUTO -all" in /etc/mdadm/mdadm.conf. I'm updating the initrd and
> rebooting after each change. I've tried "msdos" as well as GPT labels on
> the disks used by the guest. In every case I've tried, it's still
> imported.
>
> I'm running Ubuntu 12.04 "Precise" on both the host and the guest.
>
> $ uname -a
> Linux HOSTNAME 3.2.0-45-generic #70-Ubuntu SMP Wed May 29 20:12:06 UTC
> 2013 x86_64 x86_64 x86_64 GNU/Linux
>
> $ mdadm --version
> mdadm - v3.2.5 - 18th May 2012
>
> Does this suggest the initrd scripts are broken on Ubuntu, am I doing
> something wrong, or is it just not possible to prevent this
> autodetection?
>
> Thanks for any insight you can provide!

Please unpack initrd [1] and check mdamd.conf there, as the initramfs
hook may generate mdadm.conf from scratch. [2]
You may want to further adjust mdadm.conf via
/etc/initramfs-tools/hooks to make it the way you need it, and make
your changes persist across kernel/initrd upgrades.

[1] cd `mktemp -d` && gzip -dc /boot/initrd.img-`uname -r` | cpio -ivd
&& cat etc/mdadm/mdadm.conf
[2] see /usr/share/initramfs-tools/hooks/mdadm

Regards,

Dmitrijs.

Re: Prevent Autodetection

[Richard Laager]

I re-tested the exact same scenarios today in what I believe was the
same way, and now it's working as expected. I'm not sure why it didn't
work before.

Sorry for the noise!

-- 
Richard