From 3482daf56bce925b75c6b2f038c4a2a4653fb9ad Mon Sep 17 00:00:00 2001 From: Matt Riedemann Date: Fri, 5 Apr 2019 17:39:13 -0400 Subject: [PATCH] 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 --- doc/source/user/aggregates.rst | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/doc/source/user/aggregates.rst b/doc/source/user/aggregates.rst index c8d8429a9f7d..74a1848dbc3f 100644 --- a/doc/source/user/aggregates.rst +++ b/doc/source/user/aggregates.rst @@ -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 `_ + * `Bug 1781421 `_ + Design ------