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<div class="moz-cite-prefix">Duncan, I don't think it's possible to
have multiple volume groups using the same physical volume[1]. In
fact, counter-intuitively (at least to me) the nesting actually
goes the other way with multiple physical volumes comprising a
single volume group. The LVM naming scheme actually makes more
sense with this hierarchy.<br>
<br>
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>
<br>
Duncan, could you please elaborate on the pain a single volume
group is likely to cause for Cinder? Is it a show stopper?<br>
<br>
Thank you,<br>
Dan<br>
<br>
1. <a class="moz-txt-link-freetext" href="https://wiki.archlinux.org/index.php/LVM#LVM_Building_Blocks">https://wiki.archlinux.org/index.php/LVM#LVM_Building_Blocks</a><br>
<br>
<br>
On 10/21/2014 03:10 PM, Duncan Thomas wrote:<br>
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<p>Sharing the vg with cinder is likely to cause some pain testing
proposed features cinder reconciling backend with the cinder db.
Creating a second vg sharing the same backend pv is easy and
avoids all such problems.</p>
<p>Duncan Thomas</p>
<div class="gmail_quote">On Oct 21, 2014 4:07 PM, "Dan Genin" <<a
moz-do-not-send="true" href="mailto:daniel.genin@jhuapl.edu">daniel.genin@jhuapl.edu</a>>
wrote:<br type="attribution">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hello,<br>
<br>
I would like to add to DevStack the ability to stand up Nova
with LVM ephemeral<br>
storage. Below is a draft of the blueprint describing the
proposed feature.<br>
<br>
Suggestions on architecture, implementation and the blueprint
in general are very<br>
welcome.<br>
<br>
Best,<br>
Dan<br>
<br>
========================<br>
Enable LVM ephemeral storage for Nova<br>
========================<br>
<br>
Currently DevStack supports only file based ephemeral storage
for Nova, e.g.,<br>
raw and qcow2. This is an obstacle to Tempest testing of Nova
with LVM ephemeral<br>
storage, which in the past has been inadvertantly broken<br>
(see for example, <a moz-do-not-send="true"
href="https://bugs.launchpad.net/nova/+bug/1373962"
target="_blank">https://bugs.launchpad.net/nova/+bug/1373962</a>),
and to Tempest<br>
testing of new features based on LVM ephemeral storage, such
as LVM ephemeral<br>
storage encryption.<br>
<br>
To enable Nova to come up with LVM ephemeral storage it must
be provided a<br>
volume group. Based on an initial discussion with Dean Troyer,
this is best<br>
achieved by creating a single volume group for all services
that potentially<br>
need LVM storage; at the moment these are Nova and Cinder.<br>
<br>
Implementation of this feature will:<br>
<br>
* move code in lib/cinder/cinder_backends/lvm to lib/lvm with
appropriate<br>
modifications<br>
<br>
* rename the Cinder volume group to something generic, e.g.,
devstack-vg<br>
<br>
* modify the Cinder initialization and cleanup code
appropriately to use<br>
the new volume group<br>
<br>
* initialize the volume group in stack.sh, shortly before
services are<br>
launched<br>
<br>
* cleanup the volume group in unstack.sh after the services
have been<br>
shutdown<br>
<br>
The question of how large to make the common Nova-Cinder
volume group in order<br>
to enable LVM ephemeral Tempest testing will have to be
explored. Although,<br>
given the tiny instance disks used in Nova Tempest tests, the
current<br>
Cinder volume group size may already be adequate.<br>
<br>
No new configuration options will be necessary, assuming the
volume group size<br>
will not be made configurable.<br>
<br>
<br>
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