Zero Superblock... any ways to recover?

Zero Superblock... any ways to recover?

[Timo.Bolse]

Hi List,

The following Problem:

I dd'ed a whole harddisk with the RAID Partitions to another harddisk. The new
harddisk was a little bit bigger than the original one. Now if i'am doing an
mdadm -E /dev/hdc on the new harddisk i get this:

pentium-test:/proc/ide # mdadm -E /dev/hdc
mdadm: No super block found on /dev/hdc (Expected magic a92b4efc, got 00000000)

There must be a way to find the superblock on the new device... is there anyone
who has a solution for this problem?

I thougt about searching for a92b4efc on the device...

Regards,
Timo

Re: Zero Superblock... any ways to recover?

[Luca Berra]

On Mon, Mar 01, 2004 at 03:23:43PM +0100, Timo.Bolse@SerNet.DE wrote:
>Hi List,
>
>The following Problem:
>
>I dd'ed a whole harddisk with the RAID Partitions to another harddisk. The new
>harddisk was a little bit bigger than the original one. Now if i'am doing an
>mdadm -E /dev/hdc on the new harddisk i get this:
>
>pentium-test:/proc/ide # mdadm -E /dev/hdc
>mdadm: No super block found on /dev/hdc (Expected magic a92b4efc, got 00000000)
>
>There must be a way to find the superblock on the new device... is there anyone
>who has a solution for this problem?
>
>I thougt about searching for a92b4efc on the device...
>
if you know the size of the old device you can find it starting at
(sector aligned) DEVICE_SIZE - 64k
since you do not give more information on how your raid was set-up prior
to this activity it is difficult to give firther help

Regards,
L.

-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
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Re: Zero Superblock... any ways to recover?

[Paul Clements]

Luca Berra wrote:
> 
> On Mon, Mar 01, 2004 at 03:23:43PM +0100, Timo.Bolse@SerNet.DE wrote:

> >pentium-test:/proc/ide # mdadm -E /dev/hdc
> >mdadm: No super block found on /dev/hdc (Expected magic a92b4efc, got 00000000)
> >
> >There must be a way to find the superblock on the new device... is there anyone
> >who has a solution for this problem?
> >
> >I thougt about searching for a92b4efc on the device...

If you know how the array was configured, you could just re-create it,
which will create a new superblock in the correct location. But if you
aren't sure, and you want to search for the superblock, you can do:

dd if=/dev/hdc bs=512 | od -A d -h | grep "4efc a92b"

That will give you the offset of the superblock.


> if you know the size of the old device you can find it starting at
> (sector aligned) DEVICE_SIZE - 64k

Actually, the superblock is going to be at:

sb_offset = size - (size % 64k) - 64k

So the superblock is actually somewhere between 64k and 128k from the
end of the (old) device.

--
Paul