Open Stack

On 10/28/2014 11:56 AM, Dean Troyer wrote:
> On Tue, Oct 28, 2014 at 9:27 AM, Dan Genin <daniel.genin at jhuapl.edu 
> <mailto:daniel.genin at jhuapl.edu>> wrote:
>
>     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.
>
>
> 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.
>
>     Duncan, could you please elaborate on the pain a single volume
>     group is likely to cause for Cinder? Is it a show stopper?
>
>
> 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.
>
> 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.
>
> dt
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.

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.

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.

Let me know what you think.
Dan

>
> -- 
>
> Dean Troyer
> dtroyer at gmail.com <mailto:dtroyer at gmail.com>
>
>
> _______________________________________________
> OpenStack-dev mailing list
> OpenStack-dev at lists.openstack.org
> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstack.org/pipermail/openstack-dev/attachments/20141028/2262184a/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 3449 bytes
Desc: S/MIME Cryptographic Signature
URL: <http://lists.openstack.org/pipermail/openstack-dev/attachments/20141028/2262184a/attachment.bin>