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On Tue, Mar 04, 2014 at 04:15:03PM +0000, Duncan Thomas wrote:
> On 28 November 2013 10:14, Daniel P. Berrange <berrange at redhat.com> wrote:
> 
> > For this specific block zero'ing case it occurred to me that it might
> > be sufficient to just invoke 'ionice dd' instead of 'dd' and give it
> > a lower I/O priority class than normal.
> 
> Excuse the thread necromancy, I've just been searching for thoughts
> about this very issue. I've merged a patch that does I/O nice, and it
> helps, but it is easy to DoS a volume server by creating and deleting
> volumes fast while maintaining a high i/o load... the zeroing never
> runs and so you run out of allocatable space.

Oh well, thanks for experimenting with this idea anyway.

> I'll take a look at writing something with more controls than dd for
> doing the zeroing...

Someone already beat you to it....

  commit 71946855591a41dcc87ef59656a8a340774eeaf2
  Author: Pádraig Brady <pbrady at redhat.com>
  Date:   Tue Feb 11 11:51:39 2014 +0000

    libvirt: support configurable wipe methods for LVM backed instances
    
    Provide configurable methods to clear these volumes.
    The new 'volume_clear' and 'volume_clear_size' options
    are the same as currently supported by cinder.
    
    * nova/virt/libvirt/imagebackend.py: Define the new options.
    * nova/virt/libvirt/utils.py (clear_logical_volume): Support the
    new options. Refactor the existing dd method out to
    _zero_logic_volume().
    * nova/tests/virt/libvirt/test_libvirt_utils.py: Add missing test cases
    for the existing clear_logical_volume code, and for the new code
    supporting the new clearing methods.
    * etc/nova/nova.conf.sample: Add the 2 new config descriptions
    to the [libvirt] section.
    
    Change-Id: I5551197f9ec89ae2f9b051696bccdeb1af2c031f
    Closes-Bug: #889299

this matches equivalent config in cinder.


Regards,
Daniel
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