Re: raid10 devices all marked as spares?!

[NeilBrown <neilb@suse.de>]

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On Tue, 29 May 2012 20:48:42 +0200 Oliver Schinagl <oliverlist@schinagl.nl>
wrote:

> On 29-05-12 20:44, Oliver Schinagl wrote:
> > <snip>
> >>>> You can recover your data by re-creating the array.
> >>>>
> >>>>     mdadm -C /dev/md2 -l10 -n2 --layout o2 --assume-clean \
> >>>>     -e 1.2  /dev/sda6 /dev/sdb6
> >>>>
> >>>> Check that I have that right - don't just assume :-)
> >>> That looks very similar to what I used to create the array with, except
> >>> the assume-clean part. I wonder however, would it not wiser to create
> >>> the array using /dev/sda6 missing thus creating a degraded array?
> >>> Atleast I'll still have the sdb6 which MAY contain the data also (since
> >>> only sda6 'apparently' has wrong state?
> >> That would be a suitable approach - arguably safer.  If you feel more
> >> comfortable with it, then that is a strong reason to follow that course.
> >
> > I have tried that on sda6 but it cannot file a filesystem when trying 
> > to mount md2. This of course is quite scary. I am now slightly 
> > doubting if my chunksize is the same as before, 128k.
> >
> > I've used the following command.
> > mdadm -C /dev/md2 -c 128 -l 10 -p o2 --assume-clean -e 1.2 -n 2 
> > --name=opt /dev/sda6 missing
> >
> > Now I could try the same on sdb6 and hope that does work, but slightly 
> > scared of loosing everything on that partition, it could be possible 
> > of course that sdb6 is the partition that has everything in the 
> > 'proper' order? I will try to losetup sdb6 with an offset and see if 
> > that is mountable.
> Also, I forgot to mention, the thing that is really strange, is that the 
> data offset is somewhere extremely strange.
> 
> Data Offset : 262144 sectors

128MB.

> 
> where sda4 and sdb5 (md0 and 1) both have 2048, which sounds common and 
> sensible.

You'll need to use an older mdadm which uses the 2048 (1MB) offset.
The next mdadm (3.3) will have a --data-offset option to make this easier to
control.  For now you need 3.2.3 or earlier.
That should make your filesystem accessible.  If it doesn't try a different
chunk size. Maybe 64, maybe 512.

NeilBrown


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