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Date: Thu, 29 Sep 2011 21:07:19 +0200
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From: Robert P <robp236@gmail.com>
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Subject: [Qemu-devel] QEMU Live Snapshots / Commiting
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Hello,

I still have a problem with the "Live Snapshot" feature of QEMU .... and
before migrating to XEN, VMware or something similare, a quick post here:

OS: Ubuntu Natty 64bit

First, i'm starting my KVM Machine with an image like this:
qemu-img create -f qcow2 -o backing_file=<NameOfBaseImage> <Snapshotname>

If i stop the KVM Machine later, and i commit <Snapshotname> into
<NameOfBaseImage>, all the new changes are in the <NameOfBaseImage>.
That would be ok.

---

The Problem:

Actually i'm trying to create "live snapshots" periodically  while the
machine is running, like this (host2Qemu is just a special function of mine
(it works), to send a string to qemu-monitor).

                host2Qemu "cont"
                host2Qemu "guest-agent-fsfreeze"
                host2Qemu "stop"

                host2Qemu "info block"
                host2Qemu "snapshot_blkdev ide0-hd0 <Snapshot1 (example)>
qcow2"

                host2Qemu "cont"
                host2Qemu "guest-agent-fsthaw"

My idea is, to commit them one by one afterwards, when the KVM Machine is
down into the BaseImage.

So, the Snapshots are beeing written, and everytime i call that function new
data is beeing written to the new "alllocated" snapshot.
BUT, committing of that live-snapshots fails, and i've no idea why ?!

I would commit it like that:
 qemu-img commit -f qcow2 <Snapshot, with KVM was started first>
qemu-img commit -f qcow2 <Snapshot1, newer>
qemu-img commit -f qcow2 <Snapshot1, more new>
...
and so on.

So in that constellation, only changes from the Snapshot, with KVM was
started are in the Base-Image.

And another question: I have a Windows XP Guest also in KVM, but the write
performance into the (qcow2 Image) (scp, rsync, e.g) Guest seems to be
pretty poor - Are there any hints or is there a special Parameter to avoid
this?
The write Performance to a Linux Guest with a similar configuration and also
qcow2 seems to very close to the "native" Performance.

Thanks.
Robert

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Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

<div class=3D"gmail_quote">Hello, <br><br>I still have a problem with the &=
quot;Live Snapshot&quot; feature of QEMU .... and before migrating to XEN, =
VMware or something similare, a quick post here: <br><br>OS: Ubuntu Natty 6=
4bit<br>
<br>First, i&#39;m starting my KVM Machine with an image like this:<br>
qemu-img create -f qcow2 -o backing_file=3D&lt;NameOfBaseImage&gt; &lt;Snap=
shotname&gt;<br><br>If i stop the KVM Machine later, and i commit &lt;Snaps=
hotname&gt; into &lt;NameOfBaseImage&gt;, all the new changes are in the &l=
t;NameOfBaseImage&gt;. <br>


That would be ok. <br><br>---<br><br>The Problem: <br><br>Actually i&#39;m =
trying to create &quot;live snapshots&quot; periodically=A0 while the machi=
ne is running, like this (host2Qemu is just a special function of mine (it =
works), to send a string to qemu-monitor). <br>


<br>=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 host2Qemu &quot;cont&quot=
;<br>=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 host2Qemu &quot;guest-ag=
ent-fsfreeze&quot;<br>=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 host2Qe=
mu &quot;stop&quot;<br><br>
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 host2Qemu &quot;info block&qu=
ot;<br>=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 host2Qemu &quot;snapsh=
ot_blkdev ide0-hd0 &lt;Snapshot1 (example)&gt; qcow2&quot;<br>
<br>=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 host2Qemu &quot;cont&quot=
;<br>
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 host2Qemu &quot;guest-agent-f=
sthaw&quot;<br><br>My idea is, to commit them one by one afterwards, when t=
he KVM Machine is down into the BaseImage. <br><br>So, the Snapshots are be=
eing written, and everytime i call that function new data is beeing written=
 to the new &quot;alllocated&quot; snapshot. <br>


BUT, committing of that live-snapshots fails, and i&#39;ve no idea why ?!<b=
r><br>I would commit it like that: <br>=A0qemu-img commit -f qcow2 &lt;Snap=
shot, with KVM was started first&gt;<br>qemu-img commit -f qcow2 &lt;Snapsh=
ot1, newer&gt;<br>


qemu-img commit -f qcow2 &lt;Snapshot1, more new&gt;<br>...<br>and so on. <=
br><br>So in that constellation, only changes from the Snapshot, with KVM w=
as started are in the Base-Image. <br>
<br>And another question: I have a Windows XP Guest also in KVM, but the wr=
ite performance into the (qcow2 Image) (scp, rsync, e.g) Guest seems to be =
pretty poor - Are there any hints or is there a special Parameter to avoid =
this? <br>


The write Performance to a Linux Guest with a similar configuration and als=
o qcow2 seems to very close to the &quot;native&quot; Performance. <br><br>=
Thanks. <br><font color=3D"#888888">Robert<br><br>
</font></div><br>

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