SilverStripe memcached multiple servers

_config.php

<?php
// Other useful changes and commands
// watch "echo stats | nc 127.0.0.1 11211"
// session.save_handler = memcache
// session.save_path = "tcp://server1:11211,tcp://server2:11211"
// $cache = SS_Cache::factory('foo'); 
// $cache->clean(Zend_Cache::CLEANING_MODE_ALL);

if (defined('MEMCACHE_SERVER_1') && defined('MEMCACHE_PORT_1')) {
	$servers = array(
				'host' => MEMCACHE_SERVER_1,
				'port' => MEMCACHE_PORT_1,
				'persistent' => true,
				'weight' => 1,
				'timeout' => 5,
				'retry_interval' => 15,
				'status' => true,
		);
}

if (defined('MEMCACHE_SERVER_2') && defined('MEMCACHE_PORT_2')) {
	$servers = array(
				'host' => MEMCACHE_SERVER_2,
				'port' => MEMCACHE_PORT_2,
				'persistent' => true,
				'weight' => 1,
				'timeout' => 5,
				'retry_interval' => 15,
				'status' => true,
		);
}

if (!empty($servers)) {
	SS_Cache::add_backend(
		'primary_memcached',
		'Memcached',
		array(
			'servers' => array($servers),
			'compression' => true,
			'compatibility' => false,
		)
	);

	SS_Cache::pick_backend('primary_memcached', 'any', 10);

}