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So, one problem here is that 'metadata' in cinder has (at least) 3
meanings. Here is an attempt to clarify (which should be on some wiki page
somewhere, I'll add it once people tell me the meaning is clear).

Volume metadata:
 - This is set via the --metadata flag at create time, and there are
interfaces to add/edit/delete it for an existing volume
 - Arbitrary key - value pairs
 - Belonging to, and controlled by, tenants
 - This should *not* be given semantic meaning by drivers, it is there for
tenants to organise and label their volumes
- A few drivers (e.g Solidfire, but there are others [1]) can read this for
semantic content. This behaviour exists for purely historical / legacy
reasons, and needs to be enabled in the config. This behaviour may be
removed in future. No new drivers should do this.
- Adding some sort of search / index of this is probably reasonable. The
glance team were talking about some sort of global metadata index, and this
would fit nicely there.

Boot metadata:
 - Called 'glance image metadata' in most of the code currently
 - Passed to nova during boot, serves the same purpose as glance metadata
in controlling the boot
    - H/W parameters
    - License keys
    - etc
 - CRUD interface proposed (Dave Chen), reviews pending
    - Needs to tie in with glance protected properties to avoid licence
systems being broken

Admin metadata:
 - Key/value pairs
 - Attached to each volume
 - Contains some driver specific stuff
 - Hidden from the tenant (might be exposed to admin)
 - No CRUD REST API currently, nor I believe a good usecase has been put
forward for one)
 - There to avoid growing the volume table indefinitely
 - Semantic meaning, possibly just for a subset of drivers
 - Exact fields in regular flux




Anybody got any questions, clarification, corrections or rants?




[1] I'm only picking on Solidfire because I know John has fairly thick skin
and so I'm unlikely to get a bunch of complains off him for it, at least
not until I've got a beer in my hand. I hope.




On 3 March 2015 at 20:25, Sasikanth Eda <sasikanth.eda at in.ibm.com> wrote:

> Hi Stackers,
>
> I am referring to one of the action item related to "metadata" discussed
> here;
>
>
> http://eavesdrop.openstack.org/meetings/cinder/2014/cinder.2014-11-19-16.00.html
>
> Can some help with the final take away (Sorry I could not find any thread
> related to its decision after this meeting).
>
> From the conversation I got a feel that supporting operations via metadata
> needs to avoided / corrected, and the operations / variations needs to be
> provided via volume_types.
>
> Is this understanding correct ?
>
> Regards,
> Sasi
>
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-- 
Duncan Thomas
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