
.. _qcow-format-ug:

Choose image format
+++++++++++++++++++

Choose whether to use the qcow2 image format for saved images.

.. image:: /_images/user_screen_shots/qcow.png
   :width: 110%

This selects the image format used for :ref:`Glance<glance-term>`
and :ref:`ephemeral volumes<ephemeral-storage-term>`.
The default setting is to use
the qcow (actually :ref:`qcow2<qcow2-term>`) format,
which is recommended when using :ref:`Swift<swift-object-storage-term>`
as the storage backend for Glance.
If you use :ref:`Ceph RBD<ceph-term>`
for Glance image storage or for ephemeral volumes,
you should disable the qcow image format
so that the raw format is used.



.. _qcow-format-ug:

Choose image format
+++++++++++++++++++

Select image format for ephemeral storage.

.. image:: /_images/user_screen_shots/qcow.png
   :width: 110%

When this option is selected, :ref:`ephemeral volumes<ephemeral-storage-term>`
will be created as a copy-on-write layer of the base image.
Without this option selected, ephemeral volumes will be full
copies of the base image. The default setting is to use
copy-on-write for ephemeral volumes. This option has no effect
when using :ref:`Ceph<ceph-term>` for ephemeral storage.

Correct description of use_cow setting
Correct description of use_cow setting

The previous description of this setting was inaccurate.
This setting refers to how ephemeral drives are handled
by Nova.

Change-Id: Ic9a534554d8cb920a38265b449e8e94984bfa28c
Closes-bug: #1375899
