Re: Corrupt Superblock on /home - semi-hijack

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On Mon, 2006-02-20 at 13:00 +0000, Anne Wilson wrote:
> On Saturday 11 February 2006 19:39, Mikkel L. Ellertson wrote:
> > If you are not going to use a specialist, there is one thing you can
> > try if you have another drive of the same type, or possible a larger
> > drive. You can use dd with the conv=noerror option to copy the
> > drive, and then use testdisk on the copy to recover things. The
> > noerror option will let dd continue after the unreadable block.
> >
> Does the new drive need preparation of any kind, formatting, for instance?
> 
To use it as a file system it must be partitioned and formatted as well
as mounted.

> I've looked at both man page and info page for dd, but both assume that you 
> know what you are doing.
> 
> > If you are fairly sure that the error is only on the first sector,
> > you you use seek=1 and skip=1 to bypass coping the first block.
> > (You have to use both, or the output will be offset 1 block.)
> >
It is not advisable to use dd for copying data from one drive to another
*unless* they are EXACTLY the same geometry. and especially when the
source is known to have errors.  The command dd used as
   "dd if=/dev/hda of=/dev/hdb"
will exactly copy the first drive to the second.  The problem becomes
that the drive hdb will now have exactly the same geometry, partiton
table, errors, etc as hda originally had, and if the drives are
physically different this may not be what you want.
 
I would recommend to use dd to copy the partition to an image file which
would work well for your needs.
   dd if=<old partitions> of=<image file> bs=32768 
is a command I use and there are no problems with doing it this way that
I am aware of.  Add the conv=noerror and other options Mikkel recommends
to prevent premature failure of the copy.
After the image file is created, it can be mounted with the loop option
and then the data moved to the new drive.
 


> Anne 
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