190 lines
8.6 KiB
ReStructuredText
190 lines
8.6 KiB
ReStructuredText
.. _volume_migration.rst:
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===============
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Migrate volumes
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===============
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OpenStack has the ability to migrate volumes between back-ends which support
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its volume-type. Migrating a volume transparently moves its data from the
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current back-end for the volume to a new one. This is an administrator
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function, and can be used for functions including storage evacuation (for
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maintenance or decommissioning), or manual optimizations (for example,
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performance, reliability, or cost).
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These workflows are possible for a migration:
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#. If the storage can migrate the volume on its own, it is given the
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opportunity to do so. This allows the Block Storage driver to enable
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optimizations that the storage might be able to perform. If the back-end
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is not able to perform the migration, the Block Storage uses one of two
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generic flows, as follows.
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#. If the volume is not attached, the Block Storage service creates a volume
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and copies the data from the original to the new volume.
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.. note::
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While most back-ends support this function, not all do. See the driver
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documentation in the `OpenStack Configuration Reference
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<http://docs.openstack.org/mitaka/config-reference/>`__ for more
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details.
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#. If the volume is attached to a VM instance, the Block Storage creates a
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volume, and calls Compute to copy the data from the original to the new
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volume. Currently this is supported only by the Compute libvirt driver.
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As an example, this scenario shows two LVM back-ends and migrates an attached
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volume from one to the other. This scenario uses the third migration flow.
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First, list the available back-ends:
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.. code-block:: console
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# cinder get-pools
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+----------+----------------------------------------------------+
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| Property | Value |
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+----------+----------------------------------------------------+
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| name | server1@lvmstorage-1#lvmstorage-1 |
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+----------+----------------------------------------------------+
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+----------+----------------------------------------------------+
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| Property | Value |
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+----------+----------------------------------------------------+
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| name | server2@lvmstorage-2#lvmstorage-2 |
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+----------+----------------------------------------------------+
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.. note::
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Only Block Storage V2 API supports :command:`get-pools`.
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You can also get available back-ends like following:
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.. code-block:: console
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# cinder-manage host list
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server1@lvmstorage-1 zone1
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server2@lvmstorage-2 zone1
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But it needs to add pool name in the end. For example,
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``server1@lvmstorage-1#zone1``.
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Next, as the admin user, you can see the current status of the volume
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(replace the example ID with your own):
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.. code-block:: console
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$ cinder show 6088f80a-f116-4331-ad48-9afb0dfb196c
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+--------------------------------+--------------------------------------+
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| Property | Value |
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+--------------------------------+--------------------------------------+
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| attachments | [...] |
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| availability_zone | zone1 |
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| bootable | False |
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| created_at | 2013-09-01T14:53:22.000000 |
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| display_description | test |
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| display_name | test |
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| id | 6088f80a-f116-4331-ad48-9afb0dfb196c |
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| metadata | {} |
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| os-vol-host-attr:host | server1@lvmstorage-1#lvmstorage-1 |
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| os-vol-mig-status-attr:migstat | None |
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| os-vol-mig-status-attr:name_id | None |
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| os-vol-tenant-attr:tenant_id | 6bdd8f41203e4149b5d559769307365e |
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| size | 2 |
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| snapshot_id | None |
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| source_volid | None |
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| status | in-use |
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| volume_type | None |
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+--------------------------------+--------------------------------------+
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Note these attributes:
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* ``os-vol-host-attr:host`` - the volume's current back-end.
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* ``os-vol-mig-status-attr:migstat`` - the status of this volume's migration
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(None means that a migration is not currently in progress).
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* ``os-vol-mig-status-attr:name_id`` - the volume ID that this volume's name
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on the back-end is based on. Before a volume is ever migrated, its name on
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the back-end storage may be based on the volume's ID (see the
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``volume_name_template`` configuration parameter). For example, if
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``volume_name_template`` is kept as the default value (``volume-%s``), your
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first LVM back-end has a logical volume named
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``volume-6088f80a-f116-4331-ad48-9afb0dfb196c``. During the course of a
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migration, if you create a volume and copy over the data, the volume get
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the new name but keeps its original ID. This is exposed by the ``name_id``
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attribute.
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.. note::
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If you plan to decommission a block storage node, you must stop the
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``cinder`` volume service on the node after performing the migration.
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On nodes that run CentOS, Fedora, openSUSE, Red Hat Enterprise Linux,
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or SUSE Linux Enterprise, run:
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.. code-block:: console
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# service openstack-cinder-volume stop
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# chkconfig openstack-cinder-volume off
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On nodes that run Ubuntu or Debian, run:
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.. code-block:: console
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# service cinder-volume stop
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# chkconfig cinder-volume off
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Stopping the cinder volume service will prevent volumes from being
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allocated to the node.
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Migrate this volume to the second LVM back-end:
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.. code-block:: console
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$ cinder migrate 6088f80a-f116-4331-ad48-9afb0dfb196c \
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server2@lvmstorage-2#lvmstorage-2
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You can use the :command:`cinder show` command to see the status of the
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migration. While migrating, the ``migstat`` attribute shows states such as
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``migrating`` or ``completing``. On error, ``migstat`` is set to None and the
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host attribute shows the original ``host``. On success, in this example, the
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output looks like:
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.. code-block:: console
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+--------------------------------+--------------------------------------+
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| Property | Value |
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+--------------------------------+--------------------------------------+
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| attachments | [...] |
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| availability_zone | zone1 |
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| bootable | False |
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| created_at | 2013-09-01T14:53:22.000000 |
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| display_description | test |
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| display_name | test |
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| id | 6088f80a-f116-4331-ad48-9afb0dfb196c |
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| metadata | {} |
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| os-vol-host-attr:host | server2@lvmstorage-2#lvmstorage-2 |
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| os-vol-mig-status-attr:migstat | None |
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| os-vol-mig-status-attr:name_id | 133d1f56-9ffc-4f57-8798-d5217d851862 |
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| os-vol-tenant-attr:tenant_id | 6bdd8f41203e4149b5d559769307365e |
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| size | 2 |
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| snapshot_id | None |
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| source_volid | None |
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| status | in-use |
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| volume_type | None |
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+--------------------------------+--------------------------------------+
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Note that ``migstat`` is None, host is the new host, and ``name_id`` holds the
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ID of the volume created by the migration. If you look at the second LVM back
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end, you find the logical volume
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``volume-133d1f56-9ffc-4f57-8798-d5217d851862``.
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.. note::
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The migration is not visible to non-admin users (for example, through the
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volume ``status``). However, some operations are not allowed while a
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migration is taking place, such as attaching/detaching a volume and
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deleting a volume. If a user performs such an action during a migration,
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an error is returned.
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.. note::
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Migrating volumes that have snapshots are currently not allowed.
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