Mine

'cache' => array(
        'enabled' => false,
        'frontend' => 'core',
        'frontendOptions' => array(
                'caching' => true,
                'cache_id_prefix' => 'xf_'
        ),
        'backend' => 'file',
        'backendOptions' => array(
                'file_name_prefix' => 'xf_'
        )
),