Re: [gentoo-desktop] System problems - some progress

[Paul Hartman <paul.hartman+gentoo@gmail.com>]

On Thu, Mar 24, 2011 at 3:38 PM, Lindsay Haisley <fmouse-gentoo@fmp.com> wrote:
> On Thu, 2011-03-24 at 15:15 -0500, Paul Hartman wrote:
>> On Thu, Mar 24, 2011 at 1:16 PM, Lindsay Haisley <fmouse-gentoo@fmp.com> wrote:
>> > The root of this problem is that on the old kernel, there are both
>> > a /dev/hda1 and a /dev/sda1.  The former is a partition on an old PATA
>> > drive, while the latter is a proper component of md0, but when
>> > everything becomes /dev/sdNx, there's an obvious conflict and the RAID
>> > subsystem is getting confused and is obviously not seeing it's sda1.
>>
>> Possible alternative is to disable raid autodetection and define the
>> arrays by UUID in /etc/mdadm.conf so hopefully the device names become
>> irrelevant at that point.
>
> This is a good idea.  I can turn off RAID autodetection in the kernel
> config and spec RAID1 instead, since the root fs isn't on a RAID array.
>
> I've found a number of references to putting UUIDs in ARRAY lines
> in /etc/mdadm.conf to define the UUID of an array, but none yet to using
> UUID specs in DEVICE lines, all of which I've found so far in the online
> literature use /dev/xxxx specs.  Before I take this step I'm going to
> find a more kernel-specific list and ask if this would be appropriate.
> I've tripped on RAID array errors before at the expense of days of work
> to reconstitute systems and their data.  I want to make sure this is
> kosher before I go there.

I was actually referring to the ARRAY lines and the array UUIDs. In
fact I don't even have a DEVICE line, man mdadm.conf says:
If no DEVICE line is present, then "DEVICE partitions containers" is assumed.

My mdadm.conf only contains 2 ARRAY lines, for my 2 raid arrays. I
also specify the metadata version, I assume you're using superblock
0.90 since you've been using autodetect and autodetect isn't supported
for newer versions.

So, mdadm scans all partitions (doesn't matter what they are named)
looking for superblocks containing the UUID of the arrays I specified.
Anything that doesn't match gets ignored for this purpose.

The mdadm manpage has this example command:

 mdadm --examine --brief --scan --config=partitions
Create a list of devices by reading /proc/partitions, scan these for
RAID superblocks, and printout a  brief listing of all that were
found.

Hopefully you can find your array UUIDs with that command (and if it
finds them, that's a good sign for it's ability to assemble the arrays
once the config file is made)

Good luck :)