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On Fri, Aug 24, 2018 at 04:20:21PM -0500, Matt Riedemann wrote:
> On 8/20/2018 10:29 AM, Matthew Booth wrote:
> > Secondly, is there any reason why we shouldn't just document then you
> > have to delete snapshots before doing a volume migration? Hopefully
> > some cinder folks or operators can chime in to let me know how to back
> > them up or somehow make them independent before doing this, at which
> > point the volume itself should be migratable?
> 
> Coincidentally the volume migration API never had API reference
> documentation. I have that here now [1]. It clearly states the preconditions
> to migrate a volume based on code in the volume API. However, volume
> migration is admin-only by default and retype (essentially like resize) is
> admin-or-owner so non-admins can do it and specify to migrate. In general I
> think it's best to have preconditions for *any* API documented, so anything
> needed to perform a retype should be documented in the API, like that the
> volume can't have snapshots.

That's where things get tricky though. There aren't really reconditions we can
have as a blanket statement with the retype API.

A retype can do a lot of different things, all dependent on what type you are
coming from and trying to go to. There are some retypes where all it does is
enable vendor flag ``foo`` on the volume with no change in any other state.
Then there are other retypes (using --migrate-policy on-demand) that completely
move the volume from one backend to another one, copying every block along the
way from the original to the new volume. It really depends on what types you
are trying to retype to.

> 
> [1] https://review.openstack.org/#/c/595379/
> 
> -- 
> 
> Thanks,
> 
> Matt
> 
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