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<div class="moz-cite-prefix">On 10/28/2014 11:56 AM, Dean Troyer
wrote:<br>
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<div class="gmail_quote">On Tue, Oct 28, 2014 at 9:27 AM, Dan
Genin <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:daniel.genin@jhuapl.edu" target="_blank">daniel.genin@jhuapl.edu</a>></span>
wrote:<br>
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<div>So this brings us back to the original proposal of
having separate backing files for Cinder and Nova
which Dean thought might take too much space.<br>
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<div>Between Cinder, Nova and Swift (and Ceph, etc)
everybody wants some loopback disk images. DevStack's
Swift and Ceph configurations assume loopback devices and
do no sharing.</div>
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<div> Duncan, could you please elaborate on the pain a
single volume group is likely to cause for Cinder? Is
it a show stopper?<br>
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<div>Back in the day, DevStack was built to configure Cinder
(and Nova Volume before that) to use a specific existing
volume group (VOLUME_GROUP_NAME) or create a loopback file
if necessary. With the help of VOLUME_NAME_PREFIX and
volume_name_template DevStack knew which logical volumes
belong to Cinder and could Do The Right Thing.</div>
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<div>With three loopback files being created, all wanting
larger and larger defaults, adding a fourth becomes Just One
More Thing. If Nova's use of LVM is similar enough to
Cinder's (uses deterministic naming for the LVs) I'm betting
we could make it work.</div>
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<div>dt</div>
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Nova's disk names are of the form
<instance-uuid>_<disk_type>. So deterministic but,
unfortunately, not necessarily predictable. It sounds like Duncan is
saying that Cinder needs a fixed prefix for testing its
functionality. I will be honest, I am not optimistic about
convincing Nova to change their disk naming scheme for the sake of
LVM testing. Far more important changes have lingered for months and
sometimes longer.<br>
<br>
It sounds like you are concerned about two issues with regard to the
separate volume groups approach: 1) potential loop device shortage
and 2) growing space demand. The second issue, it seems to me, will
arise no matter which of the two solutions we choose. More space
will be required for testing Nova's LVM functionality one way or
another, although, using a shared volume group would permit a more
efficient use of the available space. The first issue is, indeed, a
direct consequence of the choice to use distinct volume groups.
However, the number of available loop devices can be increased by
passing the appropriate boot parameter to the kernel, which can be
easy or hard depending on how the test VMs are spun up.<br>
<br>
I am not saying that we should necessarily go the way of separate
volume groups but, assuming for the moment that changing Nova's disk
naming scheme is not an option, we need to figure out what will
bring the least amount of pain forcing Cinder tests to work around
Nova volumes or create separate volume groups.<br>
<br>
Let me know what you think.<br>
Dan<br>
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-- <br>
<br>
Dean Troyer<br>
<a moz-do-not-send="true" href="mailto:dtroyer@gmail.com">dtroyer@gmail.com</a><br>
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