Re: [gentoo-user] ext3 partition dissapeared :(

[jcd <jcd@seznam.cz>]

Alan McKinnon píše v Út 23. 01. 2007 v 21:55 +0100:
> On Tuesday 23 January 2007 19:47, Hans-Werner Hilse wrote:
> 
> > Did you reboot between changing the partition layout and creating
> > that new partition (and moving data)? Otherwise the kernel wouldn't
> > be aware of the new partition layout. Well, if everything you wrote
> > is correct, that data should have ended up on that former Windows
> > partition and that partition should now be an ext3 one. But if you
> > just didn't care and mounted the old linux partition (sdb2 at that
> > point in time before the new partition layout), copied data and you
> > _then_ rebooted -- then you would have written your data to a
> > partition that was only a reminiscence in the kernel's structures and
> > not
> > corresponding to what cfdisk wrote to the HD. That would be an
> > explanation why the next boot failed.
> >
> > > When I do "mount /dev/sdb1 /mnt/zaloha" at /mnt/zaloha I see that
> > > old Windows NTFS partition that I already deleted (There are
> > > "Program Files", "WINDOWS", ...). I don't understand why (somewhere
> > > I read that ext3 start writing at the middle of the disk space to
> > > prevent defragmentation).
> >
> > Deleting the partition is something that only affects the boot
> > sector. Ext3 should in fact have overwritten this with it's first
> > superblock. So the mkext2fs you issued did definitively hit the wrong
> > partition.
> >
> > So my suggestion is: try "gpart -w ext2,1.5 /dev/sdb" to find your
> > partition (even better: write back the backup you've made from the
> > old partition table. Errrm...)
> 
> Some background here to elaborate on what Hans has said:
> 
> It looks like when you moved the data onto the new partition, it got 
> written somewhere on the disk. However, the kernel's idea of how the 
> partitions are laid out at that time and what fdisk just wrote to the 
> disk probably don't agree and the kernel had got it wrong.... This does 
> happen when you delete two or more partitions and create one large one.
> 
> That's the bad news. The good news is that unless you did something to 
> wipe the disk clean, the data is there somewhere and you need to find 
> it. Hans' gpart command will search the disk looking for the sequence 
> of data that is found at the start of a filesystem, and will then make 
> a smart estimate as to what the partition ought to look like.
> 
> The next good news is that you can create and delete partitions many 
> times and still get the data back intact as long as you don't overwrite 
> it. fdisk updates the partition table right at the start of the disk 
> and does nothing else so you can always undo these changes. Until you 
> are happy that everything is back it will be smart to mount this 
> partition read-only so it can't be changed:
> 
> mount -o rw /dev/sdb1 /path/to/mount/point
> 
> You say in your original mail that after moving the data "everything was 
> fine". What exactly do you mean by that:
> 
> 1. The command ended without failure so you assume it moved stuff 
> correctly, or
> 2. You proved the move was done by mounting the partition and all your 
> files were there, or
> 3. Some other reason?
> 
> alan
> 



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