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5.5. Cold migrating an instance

Cold migrating an instance involves stopping the instance and moving it to another Compute node. Cold migration facilitates migration scenarios that live migrating cannot facilitate, such as migrating instances that use PCI passthrough or Single-Root Input/Output Virtualization (SR-IOV). The scheduler automatically selects the destination Compute node. For more information, see Migration Constraints.

注記

During cold migrations, the Compute service rebuilds the migrated instances from scratch, and adjusts the machine type to the machine type of the destination Compute node. Therefore, if you cold migrate an instance with a RHEL-7.5 machine type running on a RHEL-7.5 Compute node, to a RHEL-7.6 Compute node, the migrated instance on the destination Compute node will have a RHEL-7.6 machine type.

Procedure

  1. To cold migrate an instance, run the following command to power off and move the instance: 

    (overcloud)$ openstack server migrate <vm> --wait
    • Replace <vm> with the name or ID of the instance to migrate.
    • Specify the --block-migration flag if migrating a locally stored volume.
  2. Wait for migration to complete. See Checking migration status to check the status of the migration.

  3. Check the status of the instance: 

    (overcloud)$ openstack server list --all-projects

    A status of "VERIFY_RESIZE" indicates you need to confirm or revert the migration:

    • If the migration worked as expected, confirm it: 

      (overcloud)$ openstack server resize --confirm <vm>`

      Replace <vm> with the name or ID of the instance to migrate. A status of "ACTIVE" indicates that the instance is ready to use.

    • If the migration did not work as expected, revert it: 

      (overcloud)$ openstack server resize --revert <vm>`

      Replace <vm> with the name or ID of the instance.

  4. Restart the instance: 

    (overcloud)$ openstack server start <vm>

    Replace <vm> with the name or ID of the instance.

When you finish migrating the instances, proceed to Completing the migration.