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how best to migrate instances when they are saved in /var/lib/nova


we have a Newton environment that works well. We have a number of compute nodes and many instances. the one thing we lack understanding of is the best way to migrate a instance to another compute node.

the "migrate" option of Horizon or the CLI does not seem to work right. It does do something, but in the end, the instance created on the new compute node is a brand new copy of the image that was used to create the instance originally. A lot like the "rebuild" option was chosen.

I'm thinking this is because the way we have storage setup. We don't have central storage nodes setup for ephemeral / running instances (cinder volume and glance images ARE on storage nodes but not ephemeral). So, instance's vHDs are saved on the compute nodes at /var/lib/nova/instances/.

Storage was done this way because of the storage IO characteristics we have to work with, on the type of compute nodes we have, and the number of very high IO instances that we have/will have.

Are there config settings that affect migrate which might help us get the "migrate" options to work? is there a process where we can easily migrate from one compute's /var/lin/nova/instances to another? what would be test best way to migrate in the environment we have?