Re: Help RAID5 reshape Oops / backup-file

[Nagilum <nagilum@nagilum.org>]

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----- Message from neilb@suse.de ---------
     Date: Mon, 15 Oct 2007 09:31:23 +1000
     From: Neil Brown <neilb@suse.de>
Reply-To: Neil Brown <neilb@suse.de>
  Subject: Re: Help RAID5 reshape Oops / backup-file
       To: Nagilum <nagilum@nagilum.org>
       Cc: linux-raid@vger.kernel.org


> On Sunday October 14, nagilum@nagilum.org wrote:
>> Can someone tell me if I'm on the right track?
>> I've now noticed the following:
>> # ~/mdadm-2.6.3/mdadm -v -A /dev/md0 /dev/sd[d-e]
>> mdadm: looking for devices for /dev/md0
>> mdadm: /dev/sdd is identified as a member of /dev/md0, slot -1.
>> mdadm: /dev/sde is identified as a member of /dev/md0, slot -1.
>> mdadm: No suitable drives found for /dev/md0
>
> Hmm... that might be useful..
>
> I just found your earlier email where you said:
>
>> After the machine came back up (on a rescue disk) I thought I'd
>> simply have to go through the process again. So I use add add the
>> new disk again.
>> Although that worked, I am now unable to resume the growing
>> process.
>
> Using "add add" again was not correct, and should not have been
> possible.
> You should have simply assembled the array with the full new set of
> devices.  Then reshape would have automatically restarted properly.
>
> Can you remember *exactly* what you did?  If I can reproduce the
> situation, I can find the best way to fix it and send you something to
> try.
>
> NeilBrown
>

----- End message from neilb@suse.de -----

Sure, here it goes:
The system is running Debian Etch ia64, kernel 2.6.18,
(since the exact versions might be important in this case I made  
copies of what I deemed to be relevant available online)
a copy of the "linux/drivers/md" folder of that particular kernel can  
be found at:
   http://www.nagilum.de/md/md

Etch comes with mdadm-2.5.6 + Debian patches.
See http://www.nagilum.de/md/mdadm-2.5.6/debian/changelog
I made the whole Debian Package available here:
  http://www.nagilum.de/md/
  - "mdadm-2.5.6" the extracted source with Debian patches applied
  -  mdadm_2.5.6-9.diff.gz the diff to mdadm_2.5.6.orig.tar.gz
  -  mdadm_2.5.6-9_i386.deb the i385 version of the package, however I  
was/am using  mdadm_2.5.6-9_ia64.deb
  - "mdadm_2.5.6-9.dsc" description file for building the .deb

The Raid was being reshaped from three to five drives when the  
shutdown was issued. I assume the shutdown went normally since the  
machine was off and there was no power interruption.
Upon booting the system it became apparent that the RAID was non functional.
The system boots off of a USB stick and then mounts its root  
filesystem from the RAID. Assembling the RAID happens within the  
initrd. The relevant scripts can be found here:  
http://www.nagilum.de/md/local-top/
I booted a rescue disk which is based on the identical Linux version.
I looked at the "mdadm -Q --detail /dev/md0" output and saw only 3 of  
the 5 disks in the RAID. Then I did (what I should not have done) the  
add of the two new disks, assuming that mdadm will touch these in a  
harmful way (without using --force) and refuse to do so if that's not  
the way to add active disk.
The disks were added but the reshape did not continue.
Up until now I can't think of anything else I did that could have  
changed something. (and "mdadm -Q --detail /dev/md0" looks the same  
ever since)
I think, what I should have done instead of adding those disks would  
have been to either use --re-add and/or update /etc/mdadm/mdadm.conf.  
But then again I never expected this to become so problematic. :(
By now I can also boot with 2.6.23 (I'll update to 2.6.23.1 shortly)  
and I have the latest mdadm tools (in parallel to the old ones).
I also build the test_stripe utility and tried a very briefly the  
"test" argument, but it wanted me to specify an existing file so I  
chickened out. ;)
Thanks a lot for looking into this!
Alex.

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