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Re: [libvirt-users] snapshot of running vm's



Dominique wrote:

> -----Original Message-----
> From: Dominique Ramaekers
> [mailto:dominique ramaekers cometal be]
> Sent: Wednesday, December 02, 2015 1:34 PM
> To: Lentes, Bernd; libvirt-ML
> Subject: RE: snapshot of running vm's
> 
> 
> 
> > -----Oorspronkelijk bericht-----
> > Van: libvirt-users-bounces redhat com [mailto:libvirt-users-
> > bounces redhat com] Namens Lentes, Bernd
> > Verzonden: dinsdag 1 december 2015 16:31
> > Aan: libvirt-ML
> > Onderwerp: [libvirt-users] snapshot of running vm's
> >
> > Hi,
> >
> > i'd like to create snapshots of my running vm's. I have several hosts
> > with
> > SLES11 SP4 64bit. I use libvirt 1.2.5-7.1 . VM's are Windows 7, SLES,
> > Ubuntu, Opensuse.
> > I use raw files for the vm's.
> > I try to orientate myself by
> > http://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit
> .
> > The hosts are backuped every night by a network based backup
> solution
> > (Legato).
> > My idea is:
> >
> > - delete any existing snapshot
> > - create a new snapshot
> > - of course before Legato arrives
> > - then Legato might come and saves my snapshot
> > - next night the same
> >
> >
> > Questions:
> > When I delete a snapshot, is it merged automatically with its base
> image ?
> No
> 
> > Or is it something I have to do explicitly (maybe via blockcommit) ?
> When using external snapshots, the procedure works like this:
> 1. Create external snapshot => a new file is created ex. 'image.qcow2'
> 2. Backup the original file ex. 'image.raw' (this file wil not change
over
> time. All writes are done on image.qcow2).
> 3. Active block commit (commits all writes done on image.qcow2 to
> image.raw and activate image.raw) 4. delete image.qcow2
> 
> If you do a test, you can check which file is in use by 'virsh
domblklist
> $VM'
> 
> > How can I get rid of the unused snapshot afterwards ? just rm ?
> > Because I'm doing a live backup do I need to create an external
> snapshot ?
> > To create an external snapshot do I have to provide --disk-only ?
> Yes. And it's advisible to also use --quiesce to flush the guests disk
cache
> (the guest agent needs to be installed and running on the guest) And
> optional use --no-metadata to make shure libvirt isn't following up on
> these snapshots. This way you can just remove the image.qcow2 with rm
> 
> > Do I have to provide --live as a parameter ?
> Yes, the snapshot is done on a live guest/disk
> 
> > I tried --quiesce but got that message:
> >
> > virsh # snapshot-create --domain sles11 --atomic --disk-only --quiesce
> > error: argument unsupported: QEMU guest agent is not configured The
> > system I'm testing with is SLES11 SP4 (host and guest).  I installed
the
> guest agent:
> >
> > vm58820-8:~ # rpm -q qemu-guest-agent
> > qemu-guest-agent-2.0.2-1.35
> > Is there something I have to configure ?
> Yes, you have to update the guest xml with 'virsh edit $VM' and enter
> these lines in the devices section <channel type='unix'>
>    <source mode='bind'>
>    <target type='virtio' name='org.qemu.guest_agent.0'/> </channel>
> 
> After this, it's possible the qemu guest agent is still not working,
edit the
> xml again and change the port number in the line to a free port (you'll
> see that for example spice is using the same controller, bus and
port...)
> <address type='virtio-serial' controller='0' bus='0' port='1'/>
> 
> 
> 
> >
> > Is this way of backup a good solution ? Is there something to improve,
> This way you backup disk state. Most of the times this will be great.
For
> some applications, this isn't sufficient.
> For instance, a Autodesk Vault Server has a SQL database and a separate
> file storage. Using Active block commit to backup will not guarantee
data
> concistancy. That's why Autodesk has its own 'best practice'. Here I
> initiate the Autodesk procedure through a powershell script (I connect
to
> the guest with telnet).
> 
> 
> > something I have to take care of ?
> > Is this backup consistent ?
> > Does that all work with libvirt 1.2.5-7.1 or do I need a more recent
> > version
> You'll need libvirt 1.2.9 or more and Qemu 2.1 (with higher qemu's I
have
> experienced some trouble...)
> 
> 
> > (what I don't like because I tried already to update my libvirt but
> > had tons of
> > dependencies) ?

Ok. I have to try.

> >
> > I know. A lot of questions. But it's a backup, and I wanted to be sure
> > that it operates properly.
> >
> > Thanks.
> >
> >

Hi Dominique,

thanks for your very clear and detailed answer.


Bernd
   

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