Open Stack

On Mon, 22 Oct 2018 11:45:55 +0800 (GMT+08:00), Boxiang Zhu wrote:
> I created a new vm and a new volume with type 'ceph'[So that the volume 
> will be created on one of two hosts. I assume that the volume created on 
> host dev at rbd-1#ceph this time]. Next step is to attach the volume to the 
> vm. At last I want to migrate the volume from host dev at rbd-1#ceph to 
> host dev at rbd-2#ceph, but it failed with the exception 
> 'NotImplementedError(_("Swap only supports host devices")'.
> 
> So that, my real problem is that is there any work to migrate 
> volume(*in-use*)(*ceph rbd*) from one host(pool) to another host(pool) 
> in the same ceph cluster?
> The difference between the spec[2] with my scope is only one is 
> *available*(the spec) and another is *in-use*(my scope).
> 
> 
> [1] http://docs.ceph.com/docs/master/rbd/rbd-openstack/
> [2] https://review.openstack.org/#/c/296150

Ah, I think I understand now, thank you for providing all of those 
details. And I think you explained it in your first email, that cinder 
supports migration of ceph volumes if they are 'available' but not if 
they are 'in-use'. Apologies that I didn't get your meaning the first time.

I see now the code you were referring to is this [3]:

if volume.status not in ('available', 'retyping', 'maintenance'):
     LOG.debug('Only available volumes can be migrated using backend '
               'assisted migration. Falling back to generic migration.')
     return refuse_to_migrate

So because your volume is not 'available', 'retyping', or 'maintenance', 
it's falling back to generic migration, which will end up with an error 
in nova because the source_path is not set in the volume config.

Can anyone from the cinder team chime in about whether the ceph volume 
migration could be expanded to allow migration of 'in-use' volumes? Is 
there a reason not to allow migration of 'in-use' volumes?

[3] 
https://github.com/openstack/cinder/blob/c42fdc470223d27850627fd4fc9d8cb15f2941f8/cinder/volume/drivers/rbd.py#L1618-L1621

Cheers,
-melanie