openstack/nova
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Merge "Mention [cinder]/cross_az_attach in the AZ docs"

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Zuul 2019-06-24 13:34:01 +00:00 committed by Gerrit Code Review
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doc/source/user/aggregates.rst
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@ -106,6 +106,34 @@ the user resizes the server, the scheduler will try to move it back to zone A
which may or may not work, e.g. if the admin deleted or renamed zone A in the
interim.
Resource affinity
~~~~~~~~~~~~~~~~~
The :oslo.config:option:`cinder.cross_az_attach` configuration option can be
used to restrict servers and the volumes attached to servers to the same
availability zone.
A typical use case for setting ``cross_az_attach=False`` is to enforce compute
and block storage affinity, for example in a High Performance Compute cluster.
By default ``cross_az_attach`` is True meaning that the volumes attached to
a server can be in a different availability zone than the server. If set to
False, then when creating a server with pre-existing volumes or attaching a
volume to a server, the server and volume zone must match otherwise the
request will fail. In addition, if the nova-compute service creates the volumes
to attach to the server during server create, it will request that those
volumes are created in the same availability zone as the server, which must
exist in the block storage (cinder) service.
As noted in the `Implications for moving servers`_ section, forcefully moving
a server to another zone could also break affinity with attached volumes.
.. note:: ``cross_az_attach=False`` is not widely used nor tested extensively
and thus suffers from some known issues:
* `Bug 1694844 <https://bugs.launchpad.net/nova/+bug/1694844>`_
* `Bug 1781421 <https://bugs.launchpad.net/nova/+bug/1781421>`_
Design
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