Bug#570516: md UUID changed

[martin f krafft]

also sprach Steve McIntyre <steve at einval.com> [2011.02.21.1259 +0100]:
> However, now when I use the 2.6.28 system I get similar problems.
> Previously-working devices are now not working. I'm seeing
> complaints all over the place that homehost definitions don't
> match when trying to assemble devices. *I* did not change anything
> here, so it suggests that something (the kernel RAID layer? mdadm
> init scripts in the initramfs?) has modified my superblocks in
> a broken way and stopped my system booting.

As the bug report (and Neil) says, this could be related to
homehost, but I cannot quite figure out how this would happen.

It is true that mdadm on Debian was using --auto-update-homehost up
until 3.0-1, because IIRC that was the only way to provide
a migration path from before-homehost to then.

Why the UUID would now change is complete outside of my knowledge
and imagination. I have never seen this problem.

> Since then, I've tried to force update of the homehost/uuid
> settings in the superblocks, but to no avail. Then I saw that
> I was on the old superblock version that didn't store the homehost
> itself.

They do store them, but as part of the UUID. However, without
--auto-update-homehost, I do not see a way in which the UUID should
be updated.

> I've only managed to get things up and running by actually
> recreating the RAID1 devices by hand, using the same settings as
> the previous devices. Scary stuff... :-( Yet if I reboot into the
> new kernel again, things fall apart again. Even on a newly-created
> v1.2 device.

Try this instead:

In initramfs, remove the /etc/mdadm/mdadm.conf file and replace it
with a scan:

  mdadm -Escpartitions > /etc/mdadm/mdadm.conf

then -A (assemble) your arrays, either individually or with -Asayes.

Then boot your system.

Once the system is up, compare the output of

  /usr/share/mdadm/mkconf

with the contents of /etc/mdadm/mdadm.conf and update the file with
the data from the command output.

When done, run

  update-initramfs -u

and now the system should boot.

This bug has been puzzling me all along, which is why I have not
been able to fix it. I am sorry it caused you grief.

-- 
 .''`.   martin f. krafft <madduck at d.o>      Related projects:
: :'  :  proud Debian developer               http://debiansystem.info
`. `'`   http://people.debian.org/~madduck    http://vcs-pkg.org
  `-  Debian - when you have better things to do than fixing systems
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