Am 12.10.2012 12:47, schrieb Stefan Hajnoczi:
On Fri, Oct 12, 2012 at 12:16 PM, Lukas Laukamp <lukas@xxxxxxxxxx> wrote:
Am 12.10.2012 12:11, schrieb Stefan Hajnoczi:
On Fri, Oct 12, 2012 at 11:17 AM, Lukas Laukamp <lukas@xxxxxxxxxx> 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?
When using rsync you can skip qcow2. Only two objects are needed:
1. The LVM volume on the host.
2. The last full backup on the backup client.
rsync compares #1 and #2 efficiently over the network and only
transfers data from #1 which has changed.
After rsync completes your full backup image is identical to the LVM
volume. Next week you can use it as the "last" image to rsync
against.
Stefan
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So I simply update the full backup, which is simply a raw file which get
mounted while the backup?
Best Regards
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