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[Qemu-devel] Request for clarification on qemu-img convert behavior zero
From: |
De Backer, Fred (Nokia - BE/Antwerp) |
Subject: |
[Qemu-devel] Request for clarification on qemu-img convert behavior zeroing target host_device |
Date: |
Thu, 13 Dec 2018 13:12:12 +0000 |
Hi,
We're using Openstack Ironic to deploy baremetal servers. During the deployment
process an agent (ironic-python-agent) running on Fedora linux uses qemu-img to
write a qcow2 file to a blockdevice.
Recently we saw a change in behavior of qemu-img. Previously we were using
Fedora 27 containing a fedora packaged version of qemu-img v2.10.2
(qemu-img-2.10.2-1.fc27.x86_64.rpm); now we use Fedora 29 containing a fedora
packaged version of qemu-img v3.0.0 (qemu-img-3.0.0-2.fc29.x86_64.rpm).
The command that is run by the ironic-python-agent (the same in both FC27 and
FC29) is: qemu-img -t directsync -O host_device /tmp/image.qcow2 /dev/sda
We observe that in Fedora 29 the qemu-img, before imaging the disk, it fully
zeroes it. Taking into account the disk size, the whole process now takes 35
minutes instead of 50 seconds. This causes the ironic-python-agent operation to
time-out. The Fedora 27 qemu-img doesn't do that.
Scanning through the qemu-img source code, we found that adding -S 0 to the
command on Fedora 29 qemu-img restores the behavior as observed in Fedora 27
qemu-img.
Looking through the changelogs of qemu I couldn't find this behavior change
documented.
Now the questions:
* Is this the expected/required behavior that qemu-img first zeroes the
complete target disk before writing the image. In other words: is this a
qemu-img bug?
* Is applying the -S 0 parameter a safe/sound/sensible thing to do to revert to
the old behavior. In other words: can I write a bug against the
ironic-python-agent to start using this parameter?
* If the behavior is expected: is there some pointer to
documentation/changelogs I can read about this?
Thanks,
Regards,
Fred De Backer
SME Video Integration Engineer,
IP/Optical Networks, Nokia
address@hidden
Nokia Bell NV I Copernicuslaan 50, 2018 Antwerpen I BTW BE 0404 621 642 RPR
Antwerpen I BNP Paribas Fortis 220-0002334-42 I IBAN BE 77 2200 0023 3442 I BIC
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>>
- [Qemu-devel] Request for clarification on qemu-img convert behavior zeroing target host_device,
De Backer, Fred (Nokia - BE/Antwerp) <=
- Re: [Qemu-devel] Request for clarification on qemu-img convert behavior zeroing target host_device, Eric Blake, 2018/12/13
- Re: [Qemu-devel] [Qemu-block] Request for clarification on qemu-img convert behavior zeroing target host_device, Kevin Wolf, 2018/12/13
- Re: [Qemu-devel] [Qemu-block] Request for clarification on qemu-img convert behavior zeroing target host_device, Eric Blake, 2018/12/13
- Re: [Qemu-devel] [Qemu-block] Request for clarification on qemu-img convert behavior zeroing target host_device, De Backer, Fred (Nokia - BE/Antwerp), 2018/12/13
- Re: [Qemu-devel] [Qemu-block] Request for clarification on qemu-img convert behavior zeroing target host_device, Nir Soffer, 2018/12/13
- Message not available
- Re: [Qemu-devel] [Qemu-block] Request for clarification on qemu-img convert behavior zeroing target host_device, De Backer, Fred (Nokia - BE/Antwerp), 2018/12/14
- Re: [Qemu-devel] [Qemu-block] Request for clarification on qemu-img convert behavior zeroing target host_device, Kevin Wolf, 2018/12/14
- Re: [Qemu-devel] [Qemu-block] Request for clarification on qemu-img convert behavior zeroing target host_device, De Backer, Fred (Nokia - BE/Antwerp), 2018/12/14
- Re: [Qemu-devel] [Qemu-block] Request for clarification on qemu-img convert behavior zeroing target host_device, Richard W.M. Jones, 2018/12/14
- Re: [Qemu-devel] [Qemu-block] Request for clarification on qemu-img convert behavior zeroing target host_device, Daniel P . Berrangé, 2018/12/14