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On Wed, 2019-01-23 at 19:34 +0100, Ignazio Cassano wrote:
> Thanks for the info. 
> Ignazio
> 
> Il giorno Mer 23 Gen 2019 19:29 melanie witt <melwittt at gmail.com> ha scritto:
> > On Wed, 23 Jan 2019 18:02:56 +0100, Ignazio Cassano 
> > <ignaziocassano at gmail.com> wrote:
> > > Manu thanks.
> > > I read a blueprint for providing quiesce function to nova api but I 
> > > cannot find it.
> > > Must I talk directly with libvirt api?
> > 
> > Quiesce was never added to the nova API as a separate function and a 
> > spec proposal to add it was last reviewed in Newton [1]. At the time of 
> > review, only one virt driver, libvirt, supported quiesce and the 
> > justification to add a new REST API that all but one driver could not 
> > support, was not compelling enough. AFAIK the libvirt driver is still 
> > the only one that supports quiesce. There were other concerns beyond 
> > that though, and they are detailed in the review.
> > 
> > As Matt Riedemann mentioned in his earlier reply on this thread [2], a 
> > quiesce step is integrated into the nova snapshot API, if the driver 
> > supports it (only libvirt). This is the only way you can quiesce an 
> > instance today.
the closest semi portable api call is pause, but unlike quiesce, pause will
also stop the execution of the vm. i say its semi portable as drivers are not required
to implement it. it does have more broad support 
https://docs.openstack.org/nova/latest/user/support-matrix.html#operation_pause
vmware,powervm and ironic being the main virt drivers missing support.

calling pause however will be a distruptive backup and would not be suitable 
in many cases. it is overkill in most cases and it also wont guarentte that the io
buffers are flushed just that no new data is written to the disks but the paused instnace
while the backup is done.
> > 
> > Cheers,
> > -melanie
> > 
> > [1] https://review.openstack.org/295595
> > [2] 
> > http://lists.openstack.org/pipermail/openstack-discuss/2019-January/001984.html
> > 
> > > Il giorno Mer 23 Gen 2019 17:01 Sean McGinnis <sean.mcginnis at gmx.com 
> > > <mailto:sean.mcginnis at gmx.com>> ha scritto:
> > > 
> > >     On Wed, Jan 23, 2019 at 04:56:24PM +0100, Ignazio Cassano wrote:
> > >      > Hello, I did not understand if you mean cinder snapshot pr netapp
> > >     snapshot.
> > >      > Any case, why, we do not need to quiesce the instance ?
> > >      > Regards
> > >      > Ignazio
> > >      >
> > > 
> > >     If being crash consistent is good enough for your needs, then you
> > >     don't. I know
> > >     some do prefer the coordinated quiescing of IO in the instance to
> > >     make sure any
> > >     in-flight transactions are flushed out and application data is more
> > >     likely to
> > >     be in a good consistent state.
> > > 
> > >     Depending on your application running in the instance, things like
> > >     databases
> > >     are pretty good at rolling back incomplete transactions, so it's
> > >     just a matter
> > >     of whether you can allow the possibility that something that was
> > >     successful in
> > >     the milliseconds before the snap was created to now be rolled back
> > >     when the
> > >     application restarts.
> > > 
> > 
> > 
> > 
> >