'Create a snapVx snapshot of a storage group.
:param array: the array serial number
:param source_group: the source group name
:param snap_name: the name of the snapshot
:param extra_specs: the extra specifications'

def create_storagegroup_snap(self, array, source_group, snap_name, extra_specs):

    payload = {'snapshotName': snap_name}
    resource_type = ('storagegroup/%(sg_name)s/snapshot' % {'sg_name': source_group})
    (status_code, job) = self.create_resource(array, REPLICATION, resource_type, payload)
    self.wait_for_job('Create    storage    group    snapVx', status_code, job, extra_specs)
