[openstack-dev] [Cinder] Confusion about the respective use cases for volume's admin_metadata, metadata and glance_image_metadata

Zhangleiqiang (Trump) zhangleiqiang at huawei.com
Thu May 8 03:08:14 UTC 2014


Thanks for the summary and detailed explanation. 

> 1. Volume metadata - this is for the tenant's own use. Cinder and nova don't
> assign meaning to it, other than treating it as stuff the tenant can set. It is
> entirely unrelated to glance_metadata

Does it means that the "volume_metadata" is something like "tagging" for volume? Users can use it to do the filtering or grouping work.

> 2. admin_metadata - this is an internal
> implementation detail for cinder to avoid every extension having to alter the
> core volume db model.

I find the original commit and decision of introducing admin_metadta according your info above. Hope it is helpful for others:

http://eavesdrop.openstack.org/meetings/cinder/2013/cinder.2013-07-17-16.00.log.txt
https://review.openstack.org/#/c/38322



----------
zhangleiqiang (Trump)

Best Regards


> -----Original Message-----
> From: Duncan Thomas [mailto:duncan.thomas at gmail.com]
> Sent: Wednesday, May 07, 2014 9:57 PM
> To: OpenStack Development Mailing List (not for usage questions)
> Subject: Re: [openstack-dev] [Cinder] Confusion about the respective use cases
> for volume's admin_metadata, metadata and glance_image_metadata
> 
> On 7 May 2014 09:36, Trump.Zhang <zhangleiqiang at gmail.com> wrote:
> > @Tripp, Thanks for your reply and info.
> >
> > I am also thinking if it is proper to add support for updating the
> > volume's glance_image_metadta to reflect the "newest status" of volume.
> >
> > However, there may be alternative ways to achieve it:
> > 1. Using the volume's metatadata
> > 2. Using the volume's admin_metadata
> >
> > So I am wondering which is the most proper method.
> 
> 
> We're suffering from a total overload of the term 'metadata' here, and there
> are 3 totally separate things that are somehow becoming mangled:
> 
> 1. Volume metadata - this is for the tenant's own use. Cinder and nova don't
> assign meaning to it, other than treating it as stuff the tenant can set. It is
> entirely unrelated to glance_metadata 2. admin_metadata - this is an internal
> implementation detail for cinder to avoid every extension having to alter the
> core volume db model. It is not the same thing as glance metadata or
> volume_metadata.
> 
> An interface to modify volume_glance_metadata sounds reasonable, however
> it is *unrelated* to the other two types of metadata. They are different things,
> not replacements or anything like that.
> 
> Glance protected properties need to be tied into the modification API somehow,
> or else it becomes a trivial way of bypassing protected properties. Hopefully a
> glance expert can pop up and suggest a way of achieving this integration.
> 
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