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Thanks John, I'm interested on your plan/idea about your R/O volume
support idea, can you share your draft thought/plan with me? What's
the benefit you means about "there are other benefits as well" in your
above mail (second section)?

Actually, I also think we can mark R/O tag on cinder (and nova) level
but for the real backend store, but this's not an exact design that
instance can write volume also even it be marked R/O tag/status.

Thanks,
Zhi Yan

On Mon, May 13, 2013 at 11:33 PM, John Griffith
<john.griffith at solidfire.com> wrote:
>
>
>
> On Mon, May 13, 2013 at 4:22 AM, lzy.dev at gmail.com <lzy.dev at gmail.com>
> wrote:
>>
>> Hi All,
>>
>> In
>> https://etherpad.openstack.org/summit-havana-cinder-multi-attach-and-ro-volumes,
>> I saw a comment there:
>> "Summit feedback: Not doing R/O volumes due to the limited hypervisor
>> that can support setting the volume to R/O, currently only KVM has
>> this capability".
>
> There was some disagreement in the group around this which you read on the
> etherpad, however IMO
> after talking to some folks with more Hypervisor experience/knowledge than
> myself I don't think some of the
> concerns that were voice were completely accurate.
>
>>
>>
>> I agree there probably have some troubles cause R/O volumes support
>> hard to implement.
>> But maybe since I have not attended the summit, nova and cinder guys
>> not notice there is a blueprint to plan to implement a cinder backend
>> driver for glance
>> (https://blueprints.launchpad.net/glance/+spec/glance-cinder-driver, I
>> proposed), so I consider the R/O volumes support can be implemented
>> gracefully.
>> Under the case, the R/O volume stored in cinder will be created as an
>> image, client can access it by glance via standard api, and nova can
>> prepare the R/W image (base on R/O volume) for the instance normally.
>>
>> And more, I consider the R/O volume support and cinder driver for
>> glance is valuable  because on nova side we can give some code changes
>> to allow nova prepare instance disk via particular COW mechanism base
>> on particular cinder backend store capability with more efficiency
>> way, such as efficient snapshot.
>>
> So the use cases you point out are exactly the types of things on my list
> when I was thinking about this, and I think there are other benefits as
> well.  I've met some resistance on this but my plan is that if I have time
> later in the cycle to bring the bp back online and work on it I fully intend
> to do so.
>
>>
>> Thanks,
>> Zhi Yan
>
>
> Thanks for the feed-back Zhi Yan.