Xen users - Oct 2007 - Using LVM snapshots to backup NTFS partitions for windows guests

Hi everyone!

I''ve been reading this list for a while and I''m thinking that
the best
way to do backups is using LVM snapshots as discussed here several
times.

The problem is that when i use a LVM logical volume as windows disk,
windows writes the partition table onto the LV so the LV itself is not
a partition - it''s a whole disk.

lvm/device-mapper does not create the partition devices in /dev so i
cannot mount/access the ntfs partitions with anything but fdisk, and i
would like to use ntfsclone or similar.

Is there any way around this?

Milan

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Milan Krstić wrote:
> lvm/device-mapper does not create the partition devices in /dev so i
> cannot mount/access the ntfs partitions with anything but fdisk, and i
> would like to use ntfsclone or similar.
>
>   
Try kpartx.

Regards,

Fajar

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> Hi everyone!
> 
> I''ve been reading this list for a while and I''m thinking
that the best
> way to do backups is using LVM snapshots as discussed here several
> times.
> 
> The problem is that when i use a LVM logical volume as windows disk,
> windows writes the partition table onto the LV so the LV itself is not
> a partition - it''s a whole disk.
> 
> lvm/device-mapper does not create the partition devices in /dev so i
> cannot mount/access the ntfs partitions with anything but fdisk, and i
> would like to use ntfsclone or similar.
> 
> Is there any way around this?
> 
In the past I have done this by using loopback with an offset, but you need to
do a few sums to get that right (eg figure out where in the disk image each
partition starts etc).

James

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On 24/10/2007, James Harper <james.harper@bendigoit.com.au>
wrote:
>
> > Hi everyone!
> >
> > I''ve been reading this list for a while and I''m
thinking that the best
> > way to do backups is using LVM snapshots as discussed here several
> > times.
> >
> > The problem is that when i use a LVM logical volume as windows disk,
> > windows writes the partition table onto the LV so the LV itself is not
> > a partition - it''s a whole disk.
> >
> > lvm/device-mapper does not create the partition devices in /dev so i
> > cannot mount/access the ntfs partitions with anything but fdisk, and i
> > would like to use ntfsclone or similar.
> >
> > Is there any way around this?
> >
>
> In the past I have done this by using loopback with an offset, but you
> need to do a few sums to get that right (eg figure out where in the disk
> image each partition starts etc).

Not very complicated. I''ve been doing that a few times in the last few
days
while trying to get CentOS 5 installer running under Debian Etch with Xen
3.0.3.

"fdisk -l -u /dev/xen/lvm-name" will give you the offsets. The
"Units = "
line will give you the multiplier (always was 512 for me).
Then you can do:

Find an available loop device:

# losetup -f
/dev/loop1

Setup the loop device with the right offset, the `expr...` backtick will
multiply the number you got from fdisk by 512:

# losetup -o `expr offset-from-fdisk \* 512` /dev/loop1 image-file-or-lvm

After that yuou can do
# mount /dev/loop1 /mnt/mount-point

This is on Debian Etch (mount package version 2.12).

Hope this helps,

--Amos


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