On Thu, Nov 12, 2009 at 10:45 AM, Bryn M. Reeves <bmr@xxxxxxxxxx> wrote:
On Thu, 2009-11-12 at 09:23 +0000, Mr. Teo En Ming (Zhang Enming) wrote:What's the point of adding a loopback device on top of the LV? Running
> Hi All,
>
> I have several Xen virtual machines within logical volumes using LVM2.
> I did not use disk images for performance reasons.
>
> Conventionally, if I want to clone my virtual machines, I have to dd
> the LV to an image file. But this consumes a lot of time and harddisk
> space.
>
> So, instead of doing that, I want to use losetup and kpartx with my
> logical volumes, which contain operating systems of virtual machines.
>
> I can backup the filesystems of a virtual machine in this way:
>
> # losetup /dev/loop1 /dev/virtualmachines/windows7-x64
kpartx on the LV itself will work just fine and this just adds an
unnecessary layer of overhead and complexity unless I am missing
something.
Assuming that the LV given above is a whole-disk image containing a DOS
> dd if=/dev/hda of=mbr.hda bs=512 count=1
>
> Because /dev/hda resides in a logical volume. The logical volume is a
> virtual harddisk for my virtual machine.
MBR partition table:
dd if=/dev/virtualmachines/windows7-x64 of=/tmp.mbr.img bs=512 count=1
You could also do the same with the loopN device that you set up
earlier, although I still don't see the need for that step.
Should work fine, just be sure to test each step so that you are
> 1) re-create the physical volume (PV)
>
> 2) re-create the volume group
>
> 3) assign the PV to the volume group
>
> 4) restore the LVM metadata, i.e. the configuration files for all the
> logical volumes
>
> 5) restore the MBR of my domU
>
> 6) restore the filesystems of my domU
confident and comfortable with it before you find yourself needing to do
this in anger.
Regards,
Bryn.
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Hi Bryn,
I have just tried an experiment without the losetup step. I have verified that it works using kpartx only.
root@sysresccd /root % kpartx -av /dev/virtualmachines/winxphome32
add map virtualmachines-winxphome32p1 (253:22): 0 104840127 linear /dev/virtualmachines/winxphome32 63
root@sysresccd /root % cd /dev/mapper
root@sysresccd /dev/mapper % ls *winxphome32*
virtualmachines-winxphome32 virtualmachines-winxphome32p1
root@sysresccd /dev/mapper % ls -al *winxphome32*
brw-rw---- 1 root disk 253, 0 2009-11-12 15:49 virtualmachines-winxphome32
brw-rw---- 1 root disk 253, 22 2009-11-12 18:47 virtualmachines-winxphome32p1
root@sysresccd /dev/mapper % ls -al *winxphome32*
brw-rw---- 1 root disk 253, 0 2009-11-12 15:49 virtualmachines-winxphome32
brw-rw---- 1 root disk 253, 22 2009-11-12 18:47 virtualmachines-winxphome32p1
root@sysresccd /dev/mapper % fdisk -l virtualmachines-winxphome32
Disk virtualmachines-winxphome32: 53.7 GB, 53687091200 bytes
255 heads, 63 sectors/track, 6527 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x2b362b35
Device Boot Start End Blocks Id System
virtualmachines-winxphome32p1 * 1 6526 52420063+ 7 HPFS/NTFS
Without the losetup and the corresponding overhead, it will speed up cloning of my virtual machines within LVs.
--
Mr. Teo En Ming (Zhang Enming) Dip(Mechatronics) BEng(Hons)(Mechanical Engineering)
Alma Maters:
(1) Singapore Polytechnic
(2) National University of Singapore
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