doc: fix disk=0 use case in flavor doc

[OpenStack Infra]

https://review.openstack.org/339034
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
Your project "openstack/nova" is set up so that we directly report the documentation bugs against it. If this needs changing, the docimpact-group option needs to be added for the project. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit 9d08e805a8889d84ff1076da2373c37057670f23
Author: Balazs Gibizer <email address hidden>
Date: Thu Jul 7 16:28:10 2016 +0200

    doc: fix disk=0 use case in flavor doc

    The 0 value of the disk parameter of the flavor is only meaningfull
    if the instance is booted from volume as in any other case the
    instance will use local disk and the scheduler will not be
    able to select the hosts based on the real image size as that
    information is not available for the scheduler.

    Change-Id: I6b3ba2fb323341071eae6b9e9f54ef833fdbaff7
    Closes-Bug: #1599787
    DocImpact: admin guide

[Matt Riedemann (mriedem)]

I'm not sure what needs updating in the admin guide for this, I already see this:

http://docs.openstack.org/admin-guide/compute-flavors.html

Disk: "Virtual root disk size in gigabytes. This is an ephemeral disk that the base image is copied into. When booting from a persistent volume it is not used. The “0” size is a special case which uses the native base image size as the size of the ephemeral root volume."

[Matt Riedemann (mriedem)]

Same here: http://docs.openstack.org/ops-guide/ops-user-facing-operations.html#flavors

[Augustina Ragwitz (auggy)]

Marked as incomplete and assigned to gibi to clarify what doc updates are needed.

[Balazs Gibizer (balazs-gibizer)]

Hi,

If you look at the path I made on the api ref https://review.openstack.org/#/c/339034/5/api-ref/source/parameters.yaml then you can see that we have a pretty serious limitation regarding size == 0:
"However in this case filter scheduler cannot
 select the compute host based on the virtual image size. Therefore
 0 should only be used for volume booted instances or for testing
 purposes.
"
I think this limitation shall be signaled through the admin guide as well.

[Sean Dague (sdague)]

This limitation should be documented in the Admin Guide

[Alexandra Settle (alexandra-settle)]

Thank you for triaging, updating the bug accordingly.

So I understand, the patch will require documenting the limitation in the Administrator's Guide.

"However in this case filter scheduler cannot
 select the compute host based on the virtual image size. Therefore
 0 should only be used for volume booted instances or for testing
 purposes."

Thanks,

Alex

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/428139

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/428139
Committed: https://git.openstack.org/cgit/openstack/openstack-manuals/commit/?id=6343afffe54bf062d738973d47cdff3e27c06b83
Submitter: Jenkins
Branch: master

commit 6343afffe54bf062d738973d47cdff3e27c06b83
Author: KATO Tomoyuki <email address hidden>
Date: Thu Feb 2 22:23:59 2017 +0900

    [admin-guide] add disk=0 use case for flavor

    Change-Id: I32bedd44e1f89d07c2e95ab1b3b65331eba91bd0
    Closes-Bug: #1625260

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/openstack-manuals 15.0.0 release.