On 10/28/2014 11:56 AM, Dean Troyer wrote:
On Tue, Oct 28, 2014 at 9:27 AM, Dan Genin <[email protected] <mailto:[email protected]>> wrote: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.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
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 [email protected] <mailto:[email protected]> _______________________________________________ OpenStack-dev mailing list [email protected] http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
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