cinder attach volume to instance failed

Issue

• we have RHOSP7 GA version deployed by using the redhat director. Currently, system is having one running compute node, and one running controller node.
  Both hosts are having fc, iscsi connection to EMC VNX arrays

• Cinder volume creation works well, But cinder attach volume from backend vnx with hang at 'attaching' status. Below error messages are observed at nova-compute.log

2015-08-21 03:32:31.055 3223 ERROR nova.compute.manager [req-2153e45b-3afc-4c59-8b06-366d5a06d24f e325ba409fd9483da6dcfcf7ac63def8 9071a9aa0ed24eb3822acca4d483ecf3 - - -] [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b] Failed to attach 9f872f03-6709-4553-8fe3-9db2e090c5ca at /dev/vdd
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b] Traceback (most recent call last):
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 4785, in _attach_volume
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     do_check_attach=False, do_driver_attach=True)
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/nova/virt/block_device.py", line 49, in wrapped
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     ret_val = method(obj, context, *args, **kwargs)
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/nova/virt/block_device.py", line 228, in attach
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     volume = volume_api.get(context, self.volume_id)
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/nova/volume/cinder.py", line 214, in wrapper
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     res = method(self, ctx, volume_id, *args, **kwargs)
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/nova/volume/cinder.py", line 286, in get
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     item = cinderclient(context).volumes.get(volume_id)
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/cinderclient/v2/volumes.py", line 234, in get
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     return self._get("/volumes/%s" % volume_id, "volume")
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/cinderclient/base.py", line 173, in _get
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     resp, body = self.api.client.get(url)
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/cinderclient/client.py", line 115, in get
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     return self._cs_request(url, 'GET', **kwargs)
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/cinderclient/client.py", line 112, in _cs_request
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     return self.request(url, method, **kwargs)
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]   File "/usr/lib/python2.7/site-packages/cinderclient/client.py", line 105, in request
2015-08-21 03:32:31.055 3223 TRACE nova.compute.manager [instance: d73cecb5-dbdf-45d8-9d09-d30021d20e3b]     raise exceptions.from_response(resp, body)