Confirmed in Icehouse.

Set up a host set on the 3Par prior to testing. It is possible to create and delete empty volumes. It is also possible to attach a volume to an instance. The failure occurs upon attempting to detach the volume, when cinder tries to clear the host from the 3Par.

2014-05-07 14:11:29.065 ERROR cinder.volume.manager [req-18d6d2cb-84bd-4781-b687-ba9f86d59a8d 4ad0ae2b173c4726b3307b5a4e8c0b74 87105c9b3b7948f39f873ba44d89826b] Unable to terminate volume connection: Conflict (HTTP 409) 77 - host is a member of a set
2014-05-07 14:11:29.065 ERROR oslo.messaging.rpc.dispatcher [req-18d6d2cb-84bd-4781-b687-ba9f86d59a8d 4ad0ae2b173c4726b3307b5a4e8c0b74 87105c9b3b7948f39f873ba44d89826b] Exception during message handling: Bad or unexpected response from the storage volume backend API: Unable to terminate volume connection: Conflict (HTTP 409) 77 - host is a member of a set
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher Traceback (most recent call last):
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 133, in _dispatch_and_reply
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher     incoming.message))
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 176, in _dispatch
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher     return self._do_dispatch(endpoint, method, ctxt, args)
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 122, in _do_dispatch
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher     result = getattr(endpoint, method)(ctxt, **new_args)
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher   File "/opt/stack/cinder/cinder/volume/manager.py", line 839, in terminate_connection
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher     raise exception.VolumeBackendAPIException(data=err_msg)
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher VolumeBackendAPIException: Bad or unexpected response from the storage volume backend API: Unable to terminate volume connection: Conflict (HTTP 409) 77 - host is a member of a set
2014-05-07 14:11:29.065 TRACE oslo.messaging.rpc.dispatcher
2014-05-07 14:11:29.066 ERROR oslo.messaging._drivers.common [req-18d6d2cb-84bd-4781-b687-ba9f86d59a8d 4ad0ae2b173c4726b3307b5a4e8c0b74 87105c9b3b7948f39f873ba44d89826b] Returning exception Bad or unexpected response from the storage volume backend API: Unable to terminate volume connection: Conflict (HTTP 409) 77 - host is a member of a set to caller
2014-05-07 14:11:29.066 ERROR oslo.messaging._drivers.common [req-18d6d2cb-84bd-4781-b687-ba9f86d59a8d 4ad0ae2b173c4726b3307b5a4e8c0b74 87105c9b3b7948f39f873ba44d89826b] ['Traceback (most recent call last):\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 133, in _dispatch_and_reply\n    incoming.message))\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 176, in _dispatch\n    return self._do_dispatch(endpoint, method, ctxt, args)\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 122, in _do_dispatch\n    result = getattr(endpoint, method)(ctxt, **new_args)\n', '  File "/opt/stack/cinder/cinder/volume/manager.py", line 839, in terminate_connection\n    raise exception.VolumeBackendAPIException(data=err_msg)\n', 'VolumeBackendAPIException: Bad or unexpected response from the storage volume backend API: Unable to terminate volume connection: Conflict (HTTP 409) 77 - host is a member of a set\n']


The same error is also seen when attempting to create a volume from an image, for the same reason.