[docs] Explain impact of "Use qcow format for images" in UI and docs

[Fabrizio Soppelsa]

We must clearly explain the option 'Use qcow format for images' in the settings pane.
Especially, how this is related to ceph.
And how this is relevant for snapshotting (the label says that with raw images, OpenStack doesn't support snaphots).

[Meg McRoberts (dreidellhasa)]

Does someone have more notes or references for what we need to add to http://docs.mirantis.com/openstack/fuel/master/user-guide.html#choose-image-format ? I will write up a qcow2 Terminology article to reference docs about qcow2...

Now that we support VMDK format and we have some support for Ceph on vCenter, does this issue expand?

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/133323

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/133323
Committed: https://git.openstack.org/cgit/stackforge/fuel-docs/commit/?id=d674907c0eac78c5b9c38a3f6d567e84244ff9de
Submitter: Jenkins
Branch: master

commit d674907c0eac78c5b9c38a3f6d567e84244ff9de
Author: Meg McRoberts <email address hidden>
Date: Fri Nov 7 17:27:31 2014 -0800

    Clarify choice between qcow2 and raw for image storage

    More work is being done in https://review.openstack.org/#/c/125592/

    Change-Id: I022dc1b09c97385ea375688ef0890d054d7f4f99
    Partial-Bug: 1375899

[Dmitry Borodaenko (angdraug)]

The docs part was addressed in:
https://review.openstack.org/133323

We still need to improve the UI for this option.

[Ryan Moe (rmoe)]

This option should be removed from the UI. It's an option that will rarely be used and just takes up space on the settings page. When images_type=default (as is the case when we're not using Ceph) use_cow_images is used to determine which image backend Nova will use. If use_cow_images is true (and images_type = 'default') then Nova will create ephemeral drives as a CoW layer from the original cached image. When it's false it will copy the entire image from the cache into the instance directory.

[Ryan Moe (rmoe)]

Fabrizio, are you good with just removing this option completely? I'm not sure what prompted the original bug report so maybe I'm missing something.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/156847

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/156847
Committed: https://git.openstack.org/cgit/stackforge/fuel-docs/commit/?id=e6050003d0265f1a5ab2dac2bf81eb21e56cd862
Submitter: Jenkins
Branch: master

commit e6050003d0265f1a5ab2dac2bf81eb21e56cd862
Author: Ryan Moe <email address hidden>
Date: Tue Feb 17 15:18:37 2015 -0800

    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

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/6.0
Review: https://review.openstack.org/161700

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/161700
Committed: https://git.openstack.org/cgit/stackforge/fuel-docs/commit/?id=50358e43d7e8cc2f2e4eb6007395b9a363cff691
Submitter: Jenkins
Branch: stable/6.0

commit 50358e43d7e8cc2f2e4eb6007395b9a363cff691
Author: Ryan Moe <email address hidden>
Date: Tue Feb 17 15:18:37 2015 -0800

    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
    (cherry picked from commit e6050003d0265f1a5ab2dac2bf81eb21e56cd862)