openstack/glance
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Doc: Add info about multi-attach volume types

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When using Cinder as Glance backend, we can run into an issue
when using the same image to create multiple resources.
Example: creating 10 bootable volumes from an image

This happens because, by default, Image-Volumes (storing the
image) does not allow to be attached multiple times causing
the issue to not being able to use the same image concurrently.

This patch adds a doc section to configure multi-attach volume
types to be used for Image-Volumes to prevent the above issue.

Change-Id: Idcfaffe0a3f1a030ccffd6a5fc5e7b6523ae015a
This commit is contained in:
Rajat Dhasmana 2024-10-18 16:34:45 +05:30
parent 2aa5bb356e
commit 7a98b9f0f6
1 changed files with 70 additions and 0 deletions
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doc/source/configuration/configuring.rst
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@ -981,6 +981,76 @@ documentation for more information.
.. end
Configuring multi-attach volume type
------------------------------------
When using Cinder as Glance backend, we store the image into an Image-Volume
residing in the ``service`` project owned by the ``glance`` user
(recommended).
When we use the image to create a volume or a server, the Image-Volume gets
attached to the Glance host and we copy the image data to the destination
whether being the volume or the server.
This workflow can cause problem when we try to create multiple resources using
the same image since Cinder volumes, by default, does not provide the ability
to attach the same volume multiple times.
This requires a special feature called
`Volume multi-attach <https://docs.openstack.org/cinder/latest/admin/volume-multiattach.html>`_
which enables the volume to be attached multiple times to same or different
host.
To enable multi-attach functionality for Image-Volumes, we can perform the
following steps:
* Create a multiattach volume type and set the ``<is> multiattach`` property
.. code-block:: console
$ openstack volume type create glance-multiattach
$ openstack volume type set --property multiattach="<is> True" glance-multiattach
.. note::
Creating a new volume type is an admin-only operation by default.
* **(OPTIONAL)** Set the ``volume_backend_name`` property
Once you create the multi-attach volume type for Glance, you should also set
the ``volume_backend_name`` property so that your Image-Volumes don't end up
in random backends based on the scheduling done by Cinder.
.. note::
This is not needed if you are going to re-use the existing volume types
created for Cinder volumes.
Ask your Cinder administrator for the right ``volume_backend_name`` to set
for your multi-attach volume type. Here we are using ``LVM_iSCSI`` as an
example.
.. code-block:: console
$ openstack volume type set glance-multiattach --property volume_backend_name=LVM_iSCSI
* Finally you need to set the multi-attach volume type as the value of
``cinder_volume_type`` config option to use it for creating Image-Volumes.
In glance-api.conf::
[DEFAULT]
# list of enabled stores identified by their property group name
enabled_backends = fast:cinder
# the default store, if not set glance-api service will not start
[glance_store]
default_backend = fast
# conf props for fast store instance
[fast]
...
cinder_volume_type = glance-multiattach
.. _configuring-multiple-cinder-storage-backend: