Cinder-volume can't start up with EMC driver

The cinder version is:
openstack-cinder-2013.1-2.el6.noarch

OS: RHEL6.4

When I try to use EMC driver to integrate EMC VNX to be cinder backend, I got following error in /var/log/cinder/volume.log

2013-05-13 14:40:52 CRITICAL [cinder] No module named emc
Traceback (most recent call last):
  File "/usr/bin/cinder-volume", line 57, in <module>
    server = service.Service.create(binary='cinder-volume')
  File "/usr/lib/python2.6/site-packages/cinder/service.py", line 435, in create
    service_name=service_name)
  File "/usr/lib/python2.6/site-packages/cinder/service.py", line 330, in __init__
    *args, **kwargs)
  File "/usr/lib/python2.6/site-packages/cinder/volume/manager.py", line 129, in __init__
    configuration=self.configuration)
  File "/usr/lib/python2.6/site-packages/cinder/openstack/common/importutils.py", line 40, in import_object
    return import_class(import_str)(*args, **kwargs)
  File "/usr/lib/python2.6/site-packages/cinder/openstack/common/importutils.py", line 30, in import_class
    __import__(mod_str)
ImportError: No module named emc

My cinder.conf :
[DEFAULT]
logdir = /var/log/cinder
state_path = /var/lib/cinder
lock_path = /var/lib/cinder/tmp
volumes_dir = /etc/cinder/volumes
iscsi_helper = tgtadm
sql_connection = mysql://cinder:cinder@127.0.0.1/cinder
rootwrap_config = /etc/cinder/rootwrap.conf
# VG based backend
#volume_name_template = volume-%s
#volume_group = cinder-volumes
verbose = True
auth_strategy = keystone

# RabbitMQ
rpc_backend = cinder.openstack.common.rpc.impl_kombu
rabbit_host = 10.68.125.11

#EMC backend driver
iscsi_target_prefix = iqn.1992-04.com.emc
iscsi_ip_address = 198.19.10.111
volume_driver = cinder.volume.emc.EMCISCSIDriver
#volume_driver = cinder.volume.emc.EMCSMISISCSIDriver

cinder_emc_config_file = /etc/cinder/cinder_emc_config.xml

[keystone_authtoken]
admin_tenant_name = service
admin_user = cinder
admin_password = password
auth_host = 10.68.125.11
auth_port = 35357
auth_protocol = http
signing_dirname = /tmp/keystone-signing-cinder

Kimi