[Fedora-xen] Re: How to Backup and Restore MBR within Logical Volumes?

Thu Nov 12 12:34:21 UTC 2009

On Thu, Nov 12, 2009 at 12:32 PM, Mr. Teo En Ming (Zhang Enming) <
space.time.universe at gmail.com> wrote:

>
>
> On Thu, Nov 12, 2009 at 10:55 AM, Mr. Teo En Ming (Zhang Enming) <
> space.time.universe at gmail.com> wrote:
>
>>
>>
>> On Thu, Nov 12, 2009 at 10:45 AM, Bryn M. Reeves <bmr at redhat.com> wrote:
>>
>>> On Thu, 2009-11-12 at 09:23 +0000, Mr. Teo En Ming (Zhang Enming) wrote:
>>> > 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
>>>
>>> What's the point of adding a loopback device on top of the LV? Running
>>> 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.
>>>
>>> > 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.
>>>
>>> Assuming that the LV given above is a whole-disk image containing a DOS
>>> 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.
>>>
>>> > 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
>>>
>>> Should work fine, just be sure to test each step so that you are
>>> confident and comfortable with it before you find yourself needing to do
>>> this in anger.
>>>
>>> Regards,
>>> Bryn.
>>>
>>>
>>> --
>>> fedora-list mailing list
>>> fedora-list at redhat.com
>>> To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list
>>> Guidelines:
>>> http://fedoraproject.org/wiki/Communicate/MailingListGuidelines
>>>
>>
>> Hi Bryn,
>>
>> I have just tried an experiment without the losetup step. I have verified
>> that it works using kpartx only.
>>
>> root at sysresccd /root % kpartx -av /dev/virtualmachines/winxphome32
>> add map virtualmachines-winxphome32p1 (253:22): 0 104840127 linear
>> /dev/virtualmachines/winxphome32 63
>> root at sysresccd /root % cd /dev/mapper
>> root at sysresccd /dev/mapper % ls *winxphome32*
>> virtualmachines-winxphome32  virtualmachines-winxphome32p1
>> root at 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 at 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 at 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
>> My Primary Blog: http://teo-en-ming-aka-zhang-enming.blogspot.com
>> My Secondary Blog: http://enmingteo.wordpress.com
>> My Youtube videos: http://www.youtube.com/user/enmingteo
>> Email: space.time.universe at gmail.com
>> Mobile Phone (Starhub Prepaid): +65-8369-2618
>> Street: Bedok Reservoir Road
>> Country: Singapore
>>
>
> Hi All,
>
> I have performed a backup of my F11 Dom0's PV (60 GB) of 3 logical volumes
> using fsarchiver with the maximum possible LZMA compression. The operation
> took 4 hours with 2 compression threads. The resulting backup archive size
> is 8.1 GB for a PV of 60 GB.
>
> My hardware specs:
>
> Intel Pentium Dual Core E6300 2.8 GHz
> Intel Desktop Board DQ45CB
> 6 GB DDR2-800 memory
>
>
> --
> Mr. Teo En Ming (Zhang Enming) Dip(Mechatronics) BEng(Hons)(Mechanical
> Engineering)
> Alma Maters:
> (1) Singapore Polytechnic
> (2) National University of Singapore
> My Primary Blog: http://teo-en-ming-aka-zhang-enming.blogspot.com
> My Secondary Blog: http://enmingteo.wordpress.com
> My Youtube videos: http://www.youtube.com/user/enmingteo
> Email: space.time.universe at gmail.com
> Mobile Phone (Starhub Prepaid): +65-8369-2618
> Street: Bedok Reservoir Road
> Country: Singapore
>

The fsarchiver command I have used is:

fsarchiver savefs -v -z 9 -j 2 /mnt/hitachi/test/test.fsa
/dev/vg_fedora11_host/lv_home /dev/vg_fedora11_host/lv_root
/dev/vg_fedora11_host/lv_var

-- 
Mr. Teo En Ming (Zhang Enming) Dip(Mechatronics) BEng(Hons)(Mechanical
Engineering)
Alma Maters:
(1) Singapore Polytechnic
(2) National University of Singapore
My Primary Blog: http://teo-en-ming-aka-zhang-enming.blogspot.com
My Secondary Blog: http://enmingteo.wordpress.com
My Youtube videos: http://www.youtube.com/user/enmingteo
Email: space.time.universe at gmail.com
Mobile Phone (Starhub Prepaid): +65-8369-2618
Street: Bedok Reservoir Road
Country: Singapore
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