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Originally the NFS driver did support snapshots, but it was implemented by 
just 'cp'ing the file containing the raw bits. This works fine (if 
inefficiently) for unattached volumes, but if you do this on an attached 
volume the snapshot won't be crash consistent at all.

It was decided that we could do better for attached volumes by switching to 
qcow2 and relying on nova to perform the snapshots. Based on this, the bad 
snapshot implementation was removed.

However, for a variety of reasons the nova-assisted snapshot implementation 
has remained unmerged for 2+ years and the NFS driver has been an exception 
to the rules for that whole time.

I would like to see that exception end in the near future with either the 
removal of the driver or the completion of the Nova-assisted snapshot 
implementation, and it doesn't really matter to me which.

There is a 3rd alternative which would be to modify the NFS driver to 
require a specific filesystem that supports snapshots (there are a few 
choices here, but definitely NOT ext4). Unfortunately those of us who work 
for storage vendors aren't motivated to make such a modification because it 
would be effectively creating more competition for ourselves. The only way 
this could happen is if someone not working for a storage vendor takes this on.

-Ben


On August 25, 2016 10:39:35 AM Erlon Cruz <sombrafam at gmail.com> wrote:

> Hi Jordan, Slade,
>
> Currently NFS driver does not support cloning neither snapshots (which are
> the base for implementing cloning). AFAIC, the NFS driver was in Cinder
> before the minimum requirements being discussed and set, so, it just stood
> there with the features it already supported.
>
> There is currently this job
> 'gate-tempest-dsvm-full-devstack-plugin-nfs-nv'[1] that by the way are
> failing in the same test you mentioned tough passing the snapshot tests
> (not shure how the configuration is doing that) and a work[2] in progress
> to support the snapshot feature.
>
> So, Jordan, I think its OK to allow tempest to skip this tests, provided
> that at least in the NFS driver, tempest isn't being an enforcement to
> Cinder minimum features requirements.
>
> Erlon
>
>
> [1]
> http://logs.openstack.org/86/147186/25/experimental/gate-tempest-dsvm-full-devstack-plugin-nfs-nv/b149960/
> [2] https://review.openstack.org/#/c/147186/
>
> On Wed, Aug 24, 2016 at 6:34 PM, Jordan Pittier <jordan.pittier at scality.com>
> wrote:
>
>>
>> On Wed, Aug 24, 2016 at 6:06 PM, Slade Baumann <baumann at us.ibm.com> wrote:
>>
>>> I am attempting to disable clone tests in tempest as they aren't
>>> functioning in NFS. But the tests test_volumes_clone.py and
>>> test_volumes_clone_negative.py don't have the "clone" feature
>>> toggle in them. I thought it obvious that if clone is disabled
>>> in tempest, the tests that simply clone should be disabled.
>>>
>>> So I put up a bug and fix for it, but have been talking with
>>> Jordan Pittier and he suggested I come to the mailing list to
>>> get this figured out.
>>>
>>> I'm not asking for reviews, unless you want to give them.
>>> I'm simply asking if this is the right way to go about this
>>> or if there is something else I need to do to get this into
>>> Tempest.
>>>
>>> Here are the bug and fix:
>>> https://bugs.launchpad.net/tempest/+bug/1615770
>>> https://review.openstack.org/#/c/358813/
>>>
>>> I would appreciate any suggestion or direction in this problem.
>>>
>>> For extra reference, the clone toggle flag was added here:
>>> https://bugs.launchpad.net/tempest/+bug/1488274
>>>
>>> Hi,
>> Thanks for starting this thread. My point about this patch is, as "volume
>> clone" is part of the core requirements [1] every Cinder drive must
>> support, I don't see a need for a feature flag. The feature flag already
>> exists, but that doesn't mean we should encourage its usage.
>>
>> Now, if this really helps the NFS driver (although I don"t know why we
>> couldn't support clone with NFS)... I don't have a strong opinion on this
>> patch.
>>
>> I -1ed the patch for consistency: I agree that there should be a minimum
>> set of features expected from a Cinder driver.
>>
>> [1] http://docs.openstack.org/developer/cinder/devref/drivers.html#core-
>> functionality
>>
>> Cheers,
>> Jordan
>>
>> <http://bit.ly/2aKbaTu>
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>>
>
>
>
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