[openstack-dev] instance migration strangeness in devstack

Dan Genin daniel.genin at jhuapl.edu
Wed Jan 15 22:40:48 UTC 2014

I think this qualifies as a development question but please let me know 
if I am wrong.

I have been trying to test instance migration in devstack by setting up 
a multi-node devstack following directions at 
http://devstack.org/guides/multinode-lab.html. I tested that indeed 
there were multiple availability zones and that it was possible to 
create instances in each. The I tried migrating an instance from one 
compute node to another using the Horizon interface (I could not find a 
way to /confirm///migration, which is a necessary step, from the command 
line). I created a test file on the instance's ephemeral disk, before 
migrating it, to verify that the data was moved to the destination 
compute node. After migration, I observed an instance with the same id 
active on the destination node but the test file was not present.

Perhaps I misunderstand how migration is supposed to work but I expected 
that the data on the ephemeral disk would be migrated with the instance. 
I suppose it could take some time for the ephemeral disk to be copied 
but then I would not expect the instance to become active on the 
destination node before the copy operation was complete.

I also noticed that the ephemeral disk on the source compute node was 
not removed after the instance was migrated, although, the instance 
directory was. Nor was the disk removed after the instance was 
destroyed. I was using LVM backend for my tests.

I can provide more information about my setup but I just wanted to check 
whether I was doing (or expecting) something obviously stupid.

Thank you,
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