openstack
/
nova
Code Issues Proposed changes

Mention [cinder]/cross_az_attach in the AZ docs 

Since the [cinder]/cross_az_attach configuration is all
about availability zones matching between servers and volumes,
we should mention it in the AZ documentation.

Change-Id: I7055104d0b9dbd7efdef6d02c18541172059724f
This commit is contained in:
Matt Riedemann 2019-04-05 17:39:13 -04:00
parent abe041ae1c
commit 3482daf56b
1 changed files with 28 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
doc/source/user/aggregates.rst
View File

@ -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
------