Re: [User Question] How to create a backup of an LVM based maschine without wasting space

[Lukas Laukamp <lukas@laukamp.me>]

Am 12.10.2012 12:11, schrieb Stefan Hajnoczi:
> On Fri, Oct 12, 2012 at 11:17 AM, Lukas Laukamp <lukas@laukamp.me> wrote:
>> Am 12.10.2012 10:58, schrieb Lukas Laukamp:
>>
>>> Am 12.10.2012 10:42, schrieb Stefan Hajnoczi:
>>>> On Fri, Oct 12, 2012 at 08:52:32AM +0200, Lukas Laukamp wrote:
>>>>> I have a simple user question. I have a few LVM based KVM guests and
>>>>> wan't to backup them to files. The simple and nasty way would be to
>>>>> create a complete output file with dd, which wastes very much space.
>>>>> So I would like to create a backup of the LVM to a file which only
>>>>> locates the space which is used on the LVM. Would be create when the
>>>>> output file would be something like a qcow2 file which could be also
>>>>> simply startet with KVM.
>>>> If the VM is not running you can use "qemu-img convert":
>>>>
>>>>     qemu-img convert -f raw -O qcow2 /dev/vg/vm001 vm001-backup.qcow2
>>>>
>>>> Note that cp(1) tries to make the destination file sparse (see the
>>>> --sparse option in the man page).  So you don't need to use qcow2, you
>>>> can use cp(1) to copy the LVM volume to a raw file.  It will not use
>>>> disk space for zero regions.
>>>>
>>>> If the VM is running you need to use LVM snapshots or stop the VM
>>>> temporarily so a crash-consistent backup can be taken.
>>>>
>>>> Stefan
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>>>
>>> Hello Stefano,
>>>
>>> thanks for the fast reply. I will test this later. In my case now it would
>>> be a offline backup. For the online backup I think about a seperated system
>>> which every day makes incremental backups and once a week a full backup. The
>>> main problem is, that the systems are in a WAN network and I need encryption
>>> between the systems. Would it be possible to do something like this: create
>>> the LVM snapshot for the backup, read this LVM snapshot with the remote
>>> backup system via ssh tunnel and save the output of this to qcow2 files on
>>> the backup system? And in which format could be the incremental backups be
>>> stored?
> Since there is a WAN link it's important to use a compact image
> representation before hitting the network. I would use qemu-img
> convert -O qcow2 on the host and only transfer the qcow2 output.  The
> qcow2 file does not contain zero regions and will therefore save a lot
> of network bandwidth compared to accessing the LVM volume over the
> WAN.
>
> If you are using rsync or another tool it's a different story.  You
> could rsync the current LVM volume on the host over the last full
> backup, it should avoid transferring image data which is already
> present in the last full backup - the result is that you only transfer
> changed data plus the rsync metadata.
>
> Stefan
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Hello Stefan,

the rsync part I don't have understood fully. So to create a qcow2 on 
the host, transfer this to the backup server will result in the weekly 
full backup. So do you mean I could use rsync to read the LVM from the 
host, compare the LVM data with the data in the qcow2 on the backup 
server and simply transfer the differences to the file? Or does it work 
on another way?

Best Regards