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@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@rbd-1#ceph to host dev@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


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