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

[Alan McKinnon <alan@linuxholdings.co.za>]

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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