Remove unnecessary steps for cold snapshots

[Vladan Popovic]

When creating cold snapshots we first stop the instance, create a snapshot of that instance, extract the snapshot to a file, delete the snapshot and bring the instance back up.
If the instance is stopped, then there's no need to create a snapshot because there's no concurrent writer, so the snapshot can be extracted directly and save us from the two unnecessary steps (creation and deletion of a snapshot).

[Guangya Liu (Jay Lau) (jay-lau-513)]

Hi Vladan, how did you take snapshot for the VM, using rest API with curl? I noticed that there is no command line for this, so just filed a bug to trace this. https://bugs.launchpad.net/nova/+bug/1242959

[Guangya Liu (Jay Lau) (jay-lau-513)]

Clear now, I think that you are using "nova image-create" for cold snapshot.

[Vladan Popovic (vpopovic)]

Jay, yes the cold snapshots are created with nova image-create.
(I probably should have added that in the description as well)

[Vladan Popovic (vpopovic)]

Here's the patch, didn't automagically appear here for some reason.
https://review.openstack.org/#/c/52363/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/52363
Committed: http://github.com/openstack/nova/commit/8c985874c7885f31871204d3f83ce547fefc5fb6
Submitter: Jenkins
Branch: master

commit 8c985874c7885f31871204d3f83ce547fefc5fb6
Author: Vladan Popovic <email address hidden>
Date: Thu Oct 17 07:41:20 2013 -0400

    Remove unnecessary steps for cold snapshots

    Up until now when we created cold snapshots we were stopping the
    instance, create an internal snapshot, extract the snapshot to a file
    and then delete the internal snapshot before bringing up the instance.

    If the instance is shut down, there's no concurrent writer, so the image
    can be directly extracted without taking an internal snapshot first,
    because the snapshot and the current state are the same.

    In this patch the creation and deletion of the internal snapshot are
    removed to eliminate the extra steps and optimize the creation of
    snapshots a bit.

    Closes-Bug: #1242819
    Closes-Bug: #1247185

    Change-Id: I429fa2e1e26aea321eecbf14edd11263fff525ae

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/havana
Review: https://review.openstack.org/78529

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/78529
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=d1356f7d2ab1fb3a91e7602153f0c8ce1073f1e5
Submitter: Jenkins
Branch: stable/havana

commit d1356f7d2ab1fb3a91e7602153f0c8ce1073f1e5
Author: QingXin Meng <email address hidden>
Date: Tue Mar 4 05:20:40 2014 -0800

    Remove unnecessary steps for cold snapshots

    Up until now when we created cold snapshots we were stopping the
    instance, create an internal snapshot, extract the snapshot to a file
    and then delete the internal snapshot before bringing up the instance.

    If the instance is shut down, there's no concurrent writer, so the image
    can be directly extracted without taking an internal snapshot first,
    because the snapshot and the current state are the same.

    In this patch the creation and deletion of the internal snapshot are
    removed to eliminate the extra steps and optimize the creation of
    snapshots a bit.

    Closes-Bug: #1242819
    Closes-Bug: #1247185

    Change-Id: I429fa2e1e26aea321eecbf14edd11263fff525ae
    (cherry picked from commit 8c985874c7885f31871204d3f83ce547fefc5fb6)