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Re: Using dd to copy a disk.

On Mon, Jul 28, 2003 at 12:53:27PM -0700, Bill Moseley wrote:
> I need to clone a disk.  The source is a 3ware hardware RAID 1 array.  
> >From Linux it looks like /dev/sda
> $ mount
> /dev/sda2 on / type xfs (rw)
> proc on /proc type proc (rw)
> devpts on /dev/pts type devpts (rw,gid=5,mode=620)
> /dev/sda5 on /tmp type xfs (rw)
> /dev/sda6 on /usr type xfs (rw)
> /dev/sda7 on /var type xfs (rw)
> /dev/sda8 on /usr/local type xfs (rw)
> /dev/sda9 on /home type xfs (rw)
> The destination is /dev/hda
> Can I build a new bare metal drive on /dev/hda using dd
>    dd if=/dev/sda of=/dev/hda
> Will that work with the hardware RAID array?  If so will it also copy 
> the MBR?

Yep. Yep. 

> The destination drive will NOT be used in a RAID array.  Also, the 
> drives in the RAID array cannot be used outside of the array due to the 
> meta data written by 3ware card.

I take objection to the term "cannot be used": 
As "harddisk-recovery.com" we'll make them work if neccesary, but
that's not really relevant now.

> Is there a better way to clone the data on my RAID array for use in a 
> stand-alone (non-raid) machine?

This is the "one command that does the job easily". 

- Make sure the destination drive is large enough. 
- It might boot, it might not. 

- Modify the /etc/fstab and /etc/lilo.conf files before rebooting. 
- Add


to Lilo.conf, mount the hda disk on /mnt and then run 
  lilo -r /mnt

(Mount at least the / and /boot partitions! Hmm. you don't have /boot,
so "/" would have to do.... )

Note that I'm recommending you run lilo while you're concerned about
the MBR. It might work, but running LILO again gives you a bigger
chance to get it to work....

I recently cloned a drive this way. Copying over the 80G took quite
some time. 

It would have been faster to just mount both sides and perform an
rsync. Note that rsync is a great tool for stuff like this: 

<partition hda to your liking>
mk<???>fs /dev/hda2
mount /dev/hda2 /mnt
rsync -vax / /mnt

should do the trick for one parttion. 

Oh, Note that you'd be copying a LIVE partition. A logging filesystem
like ext3 or XFS will take care in writing stuff to the drive in the
right order. You're screwing that up by just copying over the
raw drive. (the OS might write onto some block that you've already
passed in your "dd", and THEN write a block that you haven't. So the
copied filesystem will have the second write, but not the first. That's
bad if that was a required ordering. I've done this lots of times without
trouble on an ext2 filesystem, and the resulting fsck never found any
trouble. I've done it once on an ext3 filesystem, and DID get into 
trouble. So be careful: It's obviously better to remount everything 
readonly before doing this.... 
	mount -n -o remount,ro / 
	mount -n -o remount,ro /tmp
	mount -n -o remount,ro /var 


** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
*-- BitWizard writes Linux device drivers for any device you may have! --*
* I didn't say it was your fault. I said I was going to blame it on you. *

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