Re: Mounting a disk using backup superblock (solved now)

[ajlewis2@intac.com]

In linux.debian.user, you wrote:
> >on Tue, Sep 04, 2001 at 05:03:08PM +0200, Stephan Hachinger
>> (Stephan.Hachinger@gmx.de) wrote:
>> >> Hello!
>> >>
>> >> Below you see a copy of the last thread I'm referring to. My HDD and
>> >> especially the superblock no.1 is heavily demaged - but I now have
>> managed
>> >> to e2fsck the partition using the backup superblock number 32768.
> Debugfs
>> >> /dev/hda2 can also show me the contents of the partition, but "mount -t
>> >> ext2 -o sb=32768 /dev/hda2 /mnt" just won't mount it and says "bad
> magic
>> >> number" etc. Can anyone please tell me what I'm missing? Does mount
>> >> calculate the superblock offset in another way or should I give up
> or???
>> I
>> >> need this data desperately as I mentioned. If anyone can help me,
> thanks
>> >> thousand times in advance.
>> >
>> >Can't help you on disk forensics, but I *strongly* recommend you image
>> >the disk to known good media before you tweak with it.  Your debug tools
>> >should work on the disk image equally as with the physical disk, with
>> >the added bonus that it's not likely to go bad (or worse).
>>
>> Hmm, if I'd only have a HDD to save the data, I would be happy :) ; then I
>> could probably do dd if=/dev/hda2 of=/dev/xyz and e2fsck -
>> b 32768 /dev/xyz, e2fsck would restore the first superblock and my
> problems
>> were gone... but I have no second hard disk which is that big :(.
>>
>> Cheers and thanks anyway,
>>
>> Stephan
> 
> OK, just wanted to tell you the solution - while the block number which must
> be given to mount is based on the blocksize which is installed on the hard
> disk (4k in my case), the block number which must be given to mount is
> calculated on a 1k-block-basis, so I had to multiply 32768*4.
> 
> Cheers,
> 
> Stephan

Gee, I thought after you ran e2fsck with a backup superblock you would just
be able to mount it as usual with 'mount -t ext2 /dev/hda2 /mnt'  I didn't
realize you would have to give it a backup superblock on the mount command. 
I thought the old superblock would be updated.

Where can I find out more about what e2fsck does when you use the backup
superblock?

Thanks
Anita