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On Tue, May 14, 2013 at 2:47 PM, lzy.dev at gmail.com <lzy.dev at gmail.com>wrote:

> John and all, about shared-volume implementation detail base on the
> R/O volume, for now, it seems there are multiple choice for us:
>
> a. Supporting R/O volume from Nova side. Ask Nova take care R/O volume
> attaching but not Cinder, use hypervisors specific method to keep the
> volume be attached in read only mode but actually the backend volume
> (in cinder) is on R/W mode. It can be implemented as shared-volume
> said "introduce a Read Only option that could be specified during
> attach". So as we know, this is not a real R/O volume.
>
> Implementing R/O control here allows Cinder/Nova to maintain unified
capabilities across all the back-ends (given that hypervisors support R/O
control over volume).


> b. Supporting R/O volume from both Cinder and Nova sides. Nova part
> just like I mentioned in above 'a' section. And in Cinder part, we can
> give a native R/O volume support capability to Cinder, in this case,
> Cinder can pass the read-write mode argument to backend
> driver/storage, that is the volume can be attached under the "real"
> read-only mode. We also have two choices here:
> i. Allow client set this "read-only" mode option in volume creating
> API calls, and cinder will not allow modify it after the volume
> creating.
>

Any use cases for this?  A lot of changes need to be done to achieve this:
modification of API; modification of all Cinder back-end drivers.

ii. Allow client mark a "read-only" flag to a volume on-demand,
> (necessary checking is needed, such as an already attached volume will
> not allow change its "read-write" mode), client can change volume from
> R/O to R/W or reverse as they needed.
>
> While this option has best flexibility, it implies the most changes
required in Cinder.  Doing R/O control on Nova/hypervisor side seems much
simpler and cleaner unless there are special use case Nova side control
isn't able to fulfill?


> What's your thoughts?
>
> Thanks,
> Zhi Yan
>
> On Tue, May 14, 2013 at 12:09 PM, John Griffith
> <john.griffith at solidfire.com> wrote:
> >
> >
> >
> > On Mon, May 13, 2013 at 9:47 PM, lzy.dev at gmail.com <lzy.dev at gmail.com>
> > wrote:
> >>
> >> Hi, Guys
> >>
> >> Form below link, it seems Xen can support R/O volume attaching also:
> >> http://backdrift.org/xen-disk-hot-add-block-device-howto
> >>
> >> "xm block-attach <Domain> <BackDev> <FrontDev> <Mode> [BackDomain]"
> >> the "mode" can be R/O and R/W (r and w).
> >>
> >> Any thoughts? if not I will update the etherpad to adding xen.
> >>
> >> Thanks,
> >> Zhi Yan
> >>
> >> On Tue, May 14, 2013 at 2:26 AM, Martin, Kurt Frederick (ESSN Storage
> >> MSDU) <kurt.f.martin at hp.com> wrote:
> >> > Thanks Alessandro, I have also updated the etherpad
> >> >
> >> > (
> https://etherpad.openstack.org/summit-havana-cinder-multi-attach-and-ro-volumes
> )
> >> > to include the latest findings regarding R/O volumes. It appears that
> a
> >> > number of hypervisors do indeed allow for setting the volumes to read
> >> > only.
> >> >
> >> > Regards,
> >> >
> >> > Kurt Martin
> >> >
> >> >
> >> >
> >> > From: Alessandro Pilotti [mailto:ap at pilotti.it]
> >> > Sent: Monday, May 13, 2013 10:46 AM
> >> > To: OpenStack Development Mailing List
> >> > Subject: Re: [openstack-dev] [cinder] About Read-Only volume support
> >> > Importance: High
> >> >
> >> >
> >> >
> >> > Hi guys,
> >> >
> >> >
> >> >
> >> > "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".
> >> >
> >> >
> >> >
> >> > Hyper-V supports mounting R/O iSCSI volumes as well.
> >> >
> >> >
> >> >
> >> > Alessandro
> >> >
> >> >
> >> >
> >> >
> >> >
> >> > On May 13, 2013, at 13:22 , 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".
> >> >
> >> > 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.
> >> >
> >> > Thanks,
> >> > Zhi Yan
> >> >
> >> > _______________________________________________
> >> > OpenStack-dev mailing list
> >> > OpenStack-dev at lists.openstack.org
> >> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> >> >
> >> >
> >> >
> >> >
> >> > _______________________________________________
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> >> > OpenStack-dev at lists.openstack.org
> >> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> >> >
> >>
> >> _______________________________________________
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> >
> >
> > Thanks Zhi Yan, I had some conversations with folks at the summit and the
> > general concensus seemed to be that it was possible.  There's a BP for
> this
> > that met a bit of objection:
> > https://blueprints.launchpad.net/cinder/+spec/shared-volume
> >
> > perhaps we can work off of that and add some details to it.
> >
> > Thanks,
> > John
> >
> > _______________________________________________
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> > OpenStack-dev at lists.openstack.org
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> >
>
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-- 
Regards
Huang Zhiteng
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