The documentation is not complete, you can also pass the weight of each server and you can use sockets if you want. In your PHP ini:
<?php
session.save_path = "/path/to/socket:0:42"
session.save_path = "/path/to/socket_x:0:42,/path/to/socket_y:0:666"
?>
And if you should ever want to access these servers in PHP:
<?php
$servers = explode(",", ini_get("session.save_path"));
$c = count($servers);
for ($i = 0; $i < $c; ++$i) {
$servers[$i] = explode(":", $servers[$i]);
}
$memcached = new \Memcached();
call_user_func_array([ $memcached, "addServers" ], $servers);
print_r($memcached->getAllKeys());
?>