i have set lock_path as /var/lib/cinder
and got rid of this exception

2013-03-20 16:42:03.772 26480 DEBUG cinder.volume.drivers.lvm [-] Updating volume status _update_volume_status /usr/lib/python2.7/dist-packages/cinder/volume/drivers/lvm.py:548
2013-03-20 16:42:03.773 26480 DEBUG cinder.utils [-] Running cmd (subprocess): sudo cinder-rootwrap /etc/cinder/rootwrap.conf vgs --noheadings --nosuffix --unit=G -o name,size,free cinder-volumes execute /usr/lib/python2.7/dist-packages/cinder/utils.py:166
2013-03-20 16:42:26.937 26480 DEBUG cinder.openstack.common.rpc.amqp [-] received {u'_context_roles': [u'admin', u'Member'], u'_msg_id': u'78e07759035a440abca7ca4bfd012018', u'_context_quota_class': None, u'_context_request_id': u'req-d2bce6cb-7c4f-4907-8151-3f513b7af7fb', u'_con
text_read_deleted': u'no', u'args': {u'connector': {u'ip': u'192.168.10.4', u'initiator': u'iqn.1993-08.org.debian:01:95a39e617950', u'host': u'vm0.lan.lo'}, u'volume_id': u'ba7cbc34-f07a-4514-be69-8a49ce8b5fa4'}, u'_context_tenant': u'8fe12af3d57b4968b33d819ee82646f4', u'_contex
t_auth_token': '<SANITIZED>', u'_context_is_admin': True, u'version': u'1.0', u'_context_project_id': u'8fe12af3d57b4968b33d819ee82646f4', u'_context_timestamp': u'2013-03-20T12:42:26.889525', u'_context_user': u'2cd01fb6c2e0438688c486069a991c3b', u'_context_user_id': u'2cd01fb6c
2e0438688c486069a991c3b', u'method': u'initialize_connection', u'_context_remote_address': u'192.168.10.4'} _safe_log /usr/lib/python2.7/dist-packages/cinder/openstack/common/rpc/common.py:195
2013-03-20 16:42:26.937 26480 DEBUG cinder.openstack.common.rpc.amqp [-] unpacked context: {'user_id': u'2cd01fb6c2e0438688c486069a991c3b', 'roles': [u'admin', u'Member'], 'timestamp': u'2013-03-20T12:42:26.889525', 'auth_token': '<SANITIZED>', 'remote_address': u'192.168.10.4', 
'quota_class': None, 'is_admin': True, 'user': u'2cd01fb6c2e0438688c486069a991c3b', 'request_id': u'req-d2bce6cb-7c4f-4907-8151-3f513b7af7fb', 'project_id': u'8fe12af3d57b4968b33d819ee82646f4', 'read_deleted': u'no', 'tenant': u'8fe12af3d57b4968b33d819ee82646f4'} _safe_log /usr/l
ib/python2.7/dist-packages/cinder/openstack/common/rpc/common.py:195
2013-03-20 16:42:26.986 26480 DEBUG cinder.openstack.common.rpc.amqp [-] received {u'_context_roles': [u'admin', u'Member'], u'_msg_id': u'3fafe32f72d84925ab22596dec54f829', u'_context_quota_class': None, u'_context_request_id': u'req-90a18d70-dccd-45d7-ba80-ec3797a62a29', u'_con
text_read_deleted': u'no', u'args': {u'instance_uuid': u'16e4baf3-e091-4b86-b33a-dcdf7c516bfb', u'mountpoint': u'vda', u'volume_id': u'ba7cbc34-f07a-4514-be69-8a49ce8b5fa4'}, u'_context_tenant': u'8fe12af3d57b4968b33d819ee82646f4', u'_context_auth_token': '<SANITIZED>', u'_contex
t_is_admin': True, u'version': u'1.0', u'_context_project_id': u'8fe12af3d57b4968b33d819ee82646f4', u'_context_timestamp': u'2013-03-20T12:42:26.964279', u'_context_user': u'2cd01fb6c2e0438688c486069a991c3b', u'_context_user_id': u'2cd01fb6c2e0438688c486069a991c3b', u'method': u'
attach_volume', u'_context_remote_address': u'192.168.10.4'} _safe_log /usr/lib/python2.7/dist-packages/cinder/openstack/common/rpc/common.py:195
2013-03-20 16:42:26.987 26480 DEBUG cinder.openstack.common.rpc.amqp [-] unpacked context: {'user_id': u'2cd01fb6c2e0438688c486069a991c3b', 'roles': [u'admin', u'Member'], 'timestamp': u'2013-03-20T12:42:26.964279', 'auth_token': '<SANITIZED>', 'remote_address': u'192.168.10.4', 
'quota_class': None, 'is_admin': True, 'user': u'2cd01fb6c2e0438688c486069a991c3b', 'request_id': u'req-90a18d70-dccd-45d7-ba80-ec3797a62a29', 'project_id': u'8fe12af3d57b4968b33d819ee82646f4', 'read_deleted': u'no', 'tenant': u'8fe12af3d57b4968b33d819ee82646f4'} _safe_log /usr/l
ib/python2.7/dist-packages/cinder/openstack/common/rpc/common.py:195
2013-03-20 16:42:26.987 DEBUG cinder.openstack.common.lockutils [req-90a18d70-dccd-45d7-ba80-ec3797a62a29 2cd01fb6c2e0438688c486069a991c3b 8fe12af3d57b4968b33d819ee82646f4] Got semaphore "ba7cbc34-f07a-4514-be69-8a49ce8b5fa4" for method "do_attach"... inner /usr/lib/python2.7/dis
t-packages/cinder/openstack/common/lockutils.py:185
2013-03-20 16:42:26.987 DEBUG cinder.openstack.common.lockutils [req-90a18d70-dccd-45d7-ba80-ec3797a62a29 2cd01fb6c2e0438688c486069a991c3b 8fe12af3d57b4968b33d819ee82646f4] Attempting to grab file lock "ba7cbc34-f07a-4514-be69-8a49ce8b5fa4" for method "do_attach"... inner /usr/li
b/python2.7/dist-packages/cinder/openstack/common/lockutils.py:189
2013-03-20 16:42:26.988 DEBUG cinder.openstack.common.lockutils [req-90a18d70-dccd-45d7-ba80-ec3797a62a29 2cd01fb6c2e0438688c486069a991c3b 8fe12af3d57b4968b33d819ee82646f4] Got file lock "ba7cbc34-f07a-4514-be69-8a49ce8b5fa4" at /var/lib/cinder/cinder-ba7cbc34-f07a-4514-be69-8a49
ce8b5fa4 for method "do_attach"... inner /usr/lib/python2.7/dist-packages/cinder/openstack/common/lockutils.py:219
2013-03-20 16:42:27.021 DEBUG cinder.openstack.common.lockutils [req-90a18d70-dccd-45d7-ba80-ec3797a62a29 2cd01fb6c2e0438688c486069a991c3b 8fe12af3d57b4968b33d819ee82646f4] Released file lock "ba7cbc34-f07a-4514-be69-8a49ce8b5fa4" at /var/lib/cinder/cinder-ba7cbc34-f07a-4514-be69-8a49ce8b5fa4 for method "do_attach"... inner /usr/lib/python2.7/dist-packages/cinder/openstack/common/lockutils.py:226

though I have got a new one (nova this time)

2013-03-20 16:42:42.492 ERROR nova.compute.manager [req-01597e98-0078-4875-9f3f-ec3aa2898a27 2cd01fb6c2e0438688c486069a991c3b 8fe12af3d57b4968b33d819ee82646f4] [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb] Instance failed to spawn
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb] Traceback (most recen
t call last):
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]   File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 1043, in _spawn
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]     block_device_info)
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]   File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 1473, in spawn
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]     block_device_info=block_device_info)
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]   File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 2261, in to_xml
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]     disk_info, rescue, block_device_info)
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]   File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 2179, in get_guest_config
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]     inst_type):
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]   File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 2032, in get_guest_storage_config
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]     info)
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]   File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 907, in volume_driver_method
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]     return method(connection_info, *args, **kwargs)
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]   File "/usr/lib/python2.7/dist-packages/nova/openstack/common/lockutils.py", line 242, in inner
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]     retval = f(*args, **kwargs)
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]   File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/volume.py", line 238, in connect_volume
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb]     % (host_device))
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb] NovaException: iSCSI device not found at /dev/disk/by-path/ip-192.168.10.4:3260-iscsi-iqn.2010-10.org.openstack:volume-ba7cbc34-f07a-4514-be69-8a49ce8b5fa4-lun-1
2013-03-20 16:42:42.492 26663 TRACE nova.compute.manager [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb] 
2013-03-20 16:42:42.764 ERROR nova.compute.manager [req-01597e98-0078-4875-9f3f-ec3aa2898a27 2cd01fb6c2e0438688c486069a991c3b 8fe12af3d57b4968b33d819ee82646f4] [instance: 16e4baf3-e091-4b86-b33a-dcdf7c516bfb] Error: ['Traceback (most recent call last):\n', '  File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 774, in _run_instance\n    injected_files, admin_password)\n', '  File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 1043, in _spawn\n    block_device_info)\n', '  File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 1473, in spawn\n    block_device_info=block_device_info)\n', '  File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 2261, in to_xml\n    disk_info, rescue, block_device_info)\n', '  File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 2179, in get_guest_config\n    inst_type):\n', '  File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 2032, in get_guest_storage_config\n    info)\n', '  File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 907, in volume_driver_method\n    return method(connection_info, *args, **kwargs)\n', '  File "/usr/lib/python2.7/dist-packages/nova/openstack/common/lockutils.py", line 242, in inner\n    retval = f(*args, **kwargs)\n', '  File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/volume.py", line 238, in connect_volume\n    % (host_device))\n', 'NovaException: iSCSI device not found at /dev/disk/by-path/ip-192.168.10.4:3260-iscsi-iqn.2010-10.org.openstack:volume-ba7cbc34-f07a-4514-be69-8a49ce8b5fa4-lun-1\n']


It makes me think, that iscsi mounted block device with created PV and VG cinder-volumes is not needed by nova
cause it seems looking for a block device...
i have no such in fact

root@vm0:~# ls -l /dev/disk/by-path/ip-192.168.10.14\:3260-iscsi-iqn.2000-01.com.synology\:ghost0.lun*
lrwxrwxrwx 1 root root  9 Mar 19 16:18 /dev/disk/by-path/ip-192.168.10.14:3260-iscsi-iqn.2000-01.com.synology:ghost0.lun0-lun-0 -> ../../sdc
lrwxrwxrwx 1 root root 10 Mar 19 16:18 /dev/disk/by-path/ip-192.168.10.14:3260-iscsi-iqn.2000-01.com.synology:ghost0.lun0-lun-0-part1 -> ../../sdc1
lrwxrwxrwx 1 root root  9 Mar 19 09:00 /dev/disk/by-path/ip-192.168.10.14:3260-iscsi-iqn.2000-01.com.synology:ghost0.lun1-lun-0 -> ../../sdb