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Date: Wed, 5 Dec 2007 21:25:03 +0000
From: "Ricardo Almeida" <ric.almeida@gmail.com>
Subject: Re: [Qemu-devel] Online image backup
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To: qemu-devel@nongnu.org

Hi,

Discalmer: I'm just a user of QEmu :) <comments bellow>

> Fabrice, that's just part of the problem.  A full automated remote
> backup service for qemu VMs should work like this:
>
>   1. send a "savevm state" command to qemu;
>   2. wait for savevm completion;

2.1 Switch to snapshot mode

>   3. perform an *online* copy (cp, rsync, whatever) of the .qcow2 image,
> while it's still running in qemu;

3.1 Pause VM
3.2 Apply snapshot changes to local and remote copy (remote must be
running something that can apply the update)
3.3 Back to normal mode

>   4. ...repeat for all running VMs.
>

[...]

> The weak spot of this configuration is the third step of backup: if you
> perform an online copy (and that's your only real choice, since you
> don't want to powerdown the VMs every night just to backup them), you
> are copying a file while it's always modifying, and chances are high
> that the copy will be corrupted (i.e. different from any state the
> original went through), since you can't perform the copy with a single read.

See the above added steps :)
Is this a bad idea?

Regards and keep up the good work :),
Ricardo Almeida