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On Fri, 19 Oct 2018 11:33:52 +0800 (GMT+08:00), Boxiang Zhu wrote:
> When I use the LVM backend to create the volume, then attach it to a vm. 
> I can migrate the volume(in-use) from one host to another. The nova 
> libvirt will call the 'rebase' to finish it. But if using ceph backend, 
> it raises exception 'Swap only supports host devices'. So now it does 
> not support to migrate volume(in-use). Does anyone do this work now? Or 
> Is there any way to let me migrate volume(in-use) with ceph backend?

What version of cinder and nova are you using?

I found this question/answer on ask.openstack.org:

https://ask.openstack.org/en/question/112954/volume-migration-fails-notimplementederror-swap-only-supports-host-devices/

and it looks like there was some work done on the cinder side [1] to 
enable migration of in-use volumes with ceph semi-recently (Queens).

On the nova side, the code looks for the source_path in the volume 
config, and if there is not one present, it raises 
NotImplementedError(_("Swap only supports host devices"). So in your 
environment, the volume configs must be missing a source_path.

If you are using at least Queens version, then there must be something 
additional missing that we would need to do to make the migration work.

[1] https://blueprints.launchpad.net/cinder/+spec/ceph-volume-migrate

Cheers,
-melanie