[linux-lvm] A way to bypass LVM and extract the raw data off?

[IpSo]

Andreas,

  dd if=/dev/hda6 bs=512 skip=6400 of=/big/backup_hda6.bin


That did the trick. It mounted no problem whatsoever! Thank you very much. Your
help has been greatly appreciated. 

Thanks also to, Holger Grothe and Petro. 

Quoting Andreas Dilger <adilger at turbolabs.com>:

> On Jan 09, 2002  13:43 -0800, IpSo wrote:
> > Quoting Andreas Dilger <adilger at turbolabs.com>:
> > > On Jan 08, 2002  19:02 -0800, IpSo wrote:
> > > > Yup! I'm confident everything as far as the reiser filesystem is
> fine,
> > > > just LVM is very confused. 
> > > > 
> > > >    Device Boot    Start       End    Blocks   Id  System
> > > > /dev/hda1   *         1       507    255496+  82  Linux swap
> > > > /dev/hda2           508     39813  19810224    5  Extended
> > > > /dev/hda5           508      4633   2079472+  83  Linux
> > > > /dev/hda6          4634     39813  17730688+  8e  Linux LVM
> > > > 
> > > > Does the LVM information take up the first 2mb or something that I
> > > > could set the offset as, so it doesn't carry over to the loopback
> file?
> > > 
> > > No, it uses a variable amount of space.
> > > 
> > > What you could do is try
> > > 
> > > od -Ad -a /dev/hda6 | grep "R   e   I   s   E   r   2   F   s"
> > > 
> > > and start your dd 65584 bytes before the address at the line this is
> > > found on (it should align to an even block boundary).
> > 
> > At the "line", I tried the command and I got about 1000+ lines that seem
> to
> > match. I assume I just try from the first line minus 65584 (3276800) like
> you 
> > said? 
> > 
> > [root at ipso big]# od -Ad -a /dev/hda6 | grep "R   e   I   s   E   r   2   F 
>  s"
> > 3342384  bs nul soh nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3383344 eot nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3424304 eot nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3498032 stx nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3547184 eot nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3616816 ack nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3706928  nl nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3825712  nl nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3842096 dc4 nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3932208 dc4 nul soh nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3944496 dc4 nul soh nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 3956784 dc4 nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > 4001840 dc4 nul stx nul   R   e   I   s   E   r   2   F   s nul nul nul
> > ...
> > 
> > dd if=/dev/hda6 bs=512 skip=3276800 of=/big/backup_hda6.bin
> > 
> > -rw-r--r--    1 root     root     16478502912 Jan  9 12:50
> backup_hda6.bin
> 
> Well, since "od" outputs a _byte_ offset, and "dd" is skipping _sectors_,
> you need to use:
> 
> dd if=/dev/hda6 bs=512 skip=6400 of=/big/backup_hda6.bin
> 
> Granted, all of these superblock copies might be in the journal, so it
> is hard to tell (with ext2/ext3 there are backup superblocks, but they
> have numbers assigned to them, so you can still find the proper start
> of the filesystem.
> 
> > I also tried: (/dev/hda)
> > dd if=/dev/hda bs=512 skip=3276800 of=/big/backup_hda6.bin
> 
> Well, this doesn't make sense, since the offset is relative to the start
> of /dev/hda6.
> 
> Cheers, Andreas
> --
> Andreas Dilger
> http://sourceforge.net/projects/ext2resize/
> http://www-mddsp.enel.ucalgary.ca/People/adilger/
> 
> 
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> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
> 


IpSo

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