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, Dan
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