How to Backup and Restore MBR within Logical Volumes?

[Mr. Teo En Ming (Zhang Enming)]

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

virtualmachines is the name of my volume group.

windows7-x64 is the logical volume.

# kpartx -av /dev/loop1

Then I would see the partitions of the virtual machine within a logical
volume, like so:

/dev/mapper/loop1p1
/dev/mapper/loop1p2
/dev/mapper/loop1p3

Now that I can access the partitions of the virtual machine within a logical
volume, I can use partimage or fsarchiver to backup the partitions (provided
the filesystem is supported by the archiver).

But the problem is that I can only backup/clone the filesystems of my
virtual machine within a logical volume. I can't backup the Master Boot
Record (MBR) of the virtual machine within a logical volume. For example,

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.

I would like to know how to backup and also restore the MBR of my virtual
machine/guest operating system/domU within a logical volume because the
losetup and kpartx procedure only allows me access to the partitions, not
the MBR. A complete backup of a virtual machine (and also a bare metal
machine) includes the MBR and all filesystems.

If there is a catastrophic failure with my logical volumes containing domUs,
I would like to

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

Please advise.

Thank you very much.

-- 
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(a)gmail.com
Mobile Phone (Starhub Prepaid): [phone]
Street: Bedok Reservoir Road
Country: Singapore

[Veli-Pekka Kestilä]

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.
>
>  # losetup /dev/loop1 /dev/virtualmachines/windows7-x64
>  windows7-x64 is the logical volume.
>  # kpartx -av /dev/loop1
>
>  Then I would see the partitions of the virtual machine within a 
>  logical volume, like so:
>
>  /dev/mapper/loop1p1
>  /dev/mapper/loop1p2
>  /dev/mapper/loop1p3
>
>  Now that I can access the partitions of the virtual machine within a 
>  logical volume, I can use partimage or fsarchiver to backup the 
>  partitions (provided the filesystem is supported by the archiver).
>
>  But the problem is that I can only backup/clone the filesystems of my 
>  virtual machine within a logical volume. I can't backup the Master 
>  Boot Record (MBR) of the virtual machine within a logical volume. For 
>  example,
>
>  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. 
You can do dd if=/dev/dev/loop1 of=mbr.dha
bs=512 count=1 to make the 
copy of the boot block.
>  I would like to know how to backup and also restore the MBR of my 
>  virtual machine/guest operating system/domU within a logical volume 
>  because the losetup and kpartx procedure only allows me access to the 
>  partitions, not the MBR. A complete backup of a virtual machine (and 
>  also a bare metal machine) includes the MBR and all filesystems.
>
>  If there is a catastrophic failure with my logical volumes containing 
>  domUs, I would like to
>
>  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
>  
Of these steps you can recreate 1,2,3 and 4 just by keeping records of 
their parameters and using normal fdisk, pvcreate, vgcreate and lvcreate 
commands.

For the things inside of lvm you can use losetup to make the loopback 
device out of the lv where you want to install the quest operating 
system and then recreate mbr from the file. Problem probably is how to 
recreate the filesystems if your backup software cannot do it. Also with 
windows protected system files can be a problem if backup software 
doesn't support them.

One thing you could of course do is to make the system restore backup 
inside of the DomU when it's running. And then boot new DomU when 
starting up and use the system backup to restore. (of course this is 
still more work that pure dd from one place to another.)

Problem is that everything else than using dd can have it fair share of 
problems. If the domU can't be offline too long, you could allocate more 
space and use the lvm:s instant cloning features (can't remember the 
name just now. ) and then use dd with gzip or bzip to make the backup 
from this clone to keep the space requirements minimum for the stored 
copies. And have minimum disruption for the DomU.

-vpk

[Mr. Teo En Ming (Zhang Enming)]

Thank you for your advice!

Is it called LVM snapshot?

-- 
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(a)gmail.com
Mobile Phone (Starhub Prepaid): [phone]
Street: Bedok Reservoir Road
Country: Singapore

2009/11/12 Veli-Pekka Kestilä <fedora(a)guagua.fi&gt;

>  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.
> >
> > # losetup /dev/loop1 /dev/virtualmachines/windows7-x64
> > windows7-x64 is the logical volume.
> > # kpartx -av /dev/loop1
> >
> > Then I would see the partitions of the virtual machine within a logical
> > volume, like so:
> >
> > /dev/mapper/loop1p1
> > /dev/mapper/loop1p2
> > /dev/mapper/loop1p3
> >
> > Now that I can access the partitions of the virtual machine within a
> > logical volume, I can use partimage or fsarchiver to backup the partitions
> > (provided the filesystem is supported by the archiver).
> >
> > But the problem is that I can only backup/clone the filesystems of my
> > virtual machine within a logical volume. I can't backup the Master Boot
> > Record (MBR) of the virtual machine within a logical volume. For example,
> >
> > 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.
> >
>  You can do dd if=/dev/dev/loop1 of=mbr.dha bs=512 count=1 to make the copy
>  of the boot block.
>
>
> > I would like to know how to backup and also restore the MBR of my virtual
> > machine/guest operating system/domU within a logical volume because the
> > losetup and kpartx procedure only allows me access to the partitions, not
> > the MBR. A complete backup of a virtual machine (and also a bare metal
> > machine) includes the MBR and all filesystems.
> >
> > If there is a catastrophic failure with my logical volumes containing
> > domUs, I would like to
> >
> > 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
> >
> >  Of these steps you can recreate 1,2,3 and 4 just by keeping records of
>  their parameters and using normal fdisk, pvcreate, vgcreate and lvcreate
>  commands.
>
>  For the things inside of lvm you can use losetup to make the loopback
>  device out of the lv where you want to install the quest operating system
>  and then recreate mbr from the file. Problem probably is how to recreate the
>  filesystems if your backup software cannot do it. Also with windows
>  protected system files can be a problem if backup software doesn't support
>  them.
>
>  One thing you could of course do is to make the system restore backup
>  inside of the DomU when it's running. And then boot new DomU when starting
>  up and use the system backup to restore. (of course this is still more work
>  that pure dd from one place to another.)
>
>  Problem is that everything else than using dd can have it fair share of
>  problems. If the domU can't be offline too long, you could allocate more
>  space and use the lvm:s instant cloning features (can't remember the name
>  just now. ) and then use dd with gzip or bzip to make the backup from this
>  clone to keep the space requirements minimum for the stored copies. And have
>  minimum disruption for the DomU.
>
>  -vpk
>
>  --
>  Fedora-xen mailing list
>  Fedora-xen(a)redhat.com
>  https://www.redhat.com/mailman/listinfo/fedora-xen
>

[Veli-Pekka Kestilä]

Mr. Teo En Ming (Zhang Enming) wrote:
>  Thank you for your advice!
>
>  Is it called LVM snapshot? 
Yes. That's what it's called for.

-vpk

PS. And please don't top post. It breaks the 'flow' of the post and 
makes it hard to read from the archives. Plus is against the list rules 
in some of the lists you are cross posting this (which is also bad). It 
would have been better to ask the question separatedly on different 
lists instead.
>      Problem is that everything else than using dd can have it fair
>      share of problems. If the domU can't be offline too long, you
>      could allocate more space and use the lvm:s instant cloning
>      features (can't remember the name just now. ) and then use dd with
>      gzip or bzip to make the backup from this clone to keep the space
>      requirements minimum for the stored copies. And have minimum
>      disruption for the DomU.
>
>      -vpk
>
>      --
>      Fedora-xen mailing list
>      Fedora-xen(a)redhat.com <mailto:[e-mail]>
>      https://www.redhat.com/mailman/listinfo/fedora-xen
>
>
>
>
>

[Mr. Teo En Ming (Zhang Enming)]

2009/11/12 Veli-Pekka Kestilä <fedora(a)guagua.fi&gt;

>  Mr. Teo En Ming (Zhang Enming) wrote:
>
> > Thank you for your advice!
> >
> > Is it called LVM snapshot?
> >
>  Yes. That's what it's called for.
>
>  -vpk
>
>  PS. And please don't top post. It breaks the 'flow' of the post and makes
>  it hard to read from the archives. Plus is against the list rules in some of
>  the lists you are cross posting this (which is also bad). It would have been
>  better to ask the question separatedly on different lists instead.
>
> >
> >
> >
> >    Problem is that everything else than using dd can have it fair
> >    share of problems. If the domU can't be offline too long, you
> >    could allocate more space and use the lvm:s instant cloning
> >    features (can't remember the name just now. ) and then use dd with
> >    gzip or bzip to make the backup from this clone to keep the space
> >    requirements minimum for the stored copies. And have minimum
> >    disruption for the DomU.
> >
> >    -vpk
> >
> >    --
> >    Fedora-xen mailing list
> >    Fedora-xen(a)redhat.com <mailto:[e-mail]>
> >
> >    https://www.redhat.com/mailman/listinfo/fedora-xen
> >
> >
> >
> >
> >
> >
>  --
>  Fedora-xen mailing list
>  Fedora-xen(a)redhat.com
>  https://www.redhat.com/mailman/listinfo/fedora-xen
>  

Thank you vpk.

I will keep that in mind when I have a new question to ask.

-- 
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(a)gmail.com
Mobile Phone (Starhub Prepaid): [phone]
Street: Bedok Reservoir Road
Country: Singapore