RAID 0, disks swapped ?

RAID 0, disks swapped ?

[c.baegert-listes]

Hi,

I had a RAID 10, crashed since a few days, made with a soft RAID 0 (/dev/md5) 
of 2 soft RAID 1 (/dev/md3 and /dev/md4). I'm using default kernel on Debian 
Etch.

I had to recreate the main RAID 0 (mdadm --create), I thought that the order 
of /dev/md3 and /dev/md4 was not important (mdadm is known to find the good 
order automatically), but it seems it took the 2 arrays in the wrong order : 
when I tried to mount it, it failed, with the message "you need to 
reiserfsck", so I made a fsck, it said "you have to rebuild-tree", I did it 
and now all my files are messed up, and it seems theye are sliced !!!

I asked for a Reiserfs specialist who said my whole partition has an offset of 
64K. And it's the chunk size of my RAID 0 !

So do you think that the order of my sub-arrays REALLY changed in the RAID 0 ? 
and do you think possible to reorder that, before retrying higher level tools 
like fsck ?

Thank you for your help !

Regards,
-- 
 
Christophe

Re: RAID 0, disks swapped ?

[Mario 'BitKoenig' Holbe]

c.baegert-listes@lixium.fr <c.baegert-listes@lixium.fr> wrote:
> I had to recreate the main RAID 0 (mdadm --create), I thought that the order 
> of /dev/md3 and /dev/md4 was not important (mdadm is known to find the good 
> order automatically),

This is true for assembling an existing RAID (provided it has a
superblock), but when you create a new one ... where should md know the
order except from what you gave it?
But... why did you have to recreate it at all?


regards
   Mario
-- 
We are the Bore. Resistance is futile. You will be bored.

Re: RAID 0, disks swapped ?

[c.baegert-listes]

Le vendredi 17 octobre 2008, vous avez écrit :
> This is true for assembling an existing RAID (provided it has a
> superblock), but when you create a new one ... where should md know the
> order except from what you gave it?
> But... why did you have to recreate it at all?

If I remember well, a re-add failed after a disk lost sync, so I had to 
re-create the RAID 1 array after stopping it, and then I had to stop the RAID 
0 before...

Regards,
-- 
 
Christophe
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Re: RAID 0, disks swapped ?

[Mario 'BitKoenig' Holbe]

c.baegert-listes@lixium.fr <c.baegert-listes@lixium.fr> wrote:
> re-create the RAID 1 array after stopping it, and then I had to stop the RAID 
> 0 before...

Yes, stop the raid0, and start it again, but why create?


regards
   Mario
-- 
The secret that the NSA could read the Iranian secrets was more
important than any specific Iranian secrets that the NSA could
read.                           -- Bruce Schneier

Re: RAID 0, disks swapped ?

[c.baegert-listes]

Le vendredi 17 octobre 2008, vous avez écrit :
> c.baegert-listes@lixium.fr <c.baegert-listes@lixium.fr> wrote:
> > re-create the RAID 1 array after stopping it, and then I had to stop the
> > RAID 0 before...
>
> Yes, stop the raid0, and start it again, but why create?

Yes, I should have tried to assemble it... Sometimes man should better not go 
to work and stay in his bed. But it's not what I did then.

Christophe
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Re: RAID 0, disks swapped ?

[Bill Davidsen]

c.baegert-listes@lixium.fr wrote:
> Hi,
>
> I had a RAID 10, crashed since a few days, made with a soft RAID 0 (/dev/md5) 
> of 2 soft RAID 1 (/dev/md3 and /dev/md4). I'm using default kernel on Debian 
> Etch.
>   

Just for educational purposes (won't help fix your problem), you had 
RAID 1+0 rather than RAID-10. See the mdadm docs for the difference. And 
reading old discussions here on the performance of RAID-10 with two far 
copies would be useful as well.

Sorry for your loss.

-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark 

Re: RAID 0, disks swapped ?

[c.baegert-listes]

Hi,

Le vendredi 17 octobre 2008, Bill Davidsen a écrit :
> Just for educational purposes (won't help fix your problem), you had
> RAID 1+0 rather than RAID-10. See the mdadm docs for the difference. And
> reading old discussions here on the performance of RAID-10 with two far
> copies would be useful as well.

Yeah, I saw them, I use directly raid10 for a few months, but this array was 
older. The good point of the RAID 1+0 solution is that I just have to repair 
a raid0 array now. But how ?

Regards,
-- 
 
Christophe
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Re: RAID 0, disks swapped ?

[Mario 'BitKoenig' Holbe]

c.baegert-listes@lixium.fr <c.baegert-listes@lixium.fr> wrote:
> older. The good point of the RAID 1+0 solution is that I just have to repair 
> a raid0 array now. But how ?

That's most likely gone - at least your data is most likely corrupted
after your reiserfsck and rebuild-tree, unless all you did did not write
to the disks (which is not very likely :)).
You could try to recreate the array in the correct order, perhaps you
can get a little back but i think its time to consult your backups,
alone to find out what's corrupted and what's not.


regards
   Mario
-- 
Damit das Mögliche entsteht, muß immer wieder das Unmögliche versucht werden.
                                                  -- Hermann Hesse

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Re: RAID 0, disks swapped ?

[c.baegert-listes]

Le vendredi 17 octobre 2008, vous avez écrit :
> You could try to recreate the array in the correct order

Is the order the number [1] or [0] in the line below ?
md5 : active raid0 md4[1] md3[0]

Regards,
-- 
Christophe
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Re: RAID 0, disks swapped ?

[Mario 'BitKoenig' Holbe]

c.baegert-listes@lixium.fr <c.baegert-listes@lixium.fr> wrote:
> Is the order the number [1] or [0] in the line below ?
> md5 : active raid0 md4[1] md3[0]

Yes, this should be the result of mdadm -C ... /dev/md5 /dev/md3 /dev/md4


regards
   Mario
-- 
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We don't believe this to be a coincidence.    -- Jeremy S. Anderson