Does the PHP sdk know all servers?

Let's say I have a 3 server cluster in couchbase 1.8. Call each server

1.1.1.1
1.1.1.2
1.1.1.3

In my php code I do this

<?php
$cb = new Couchbase("1.1.1.1:8091"); // uses the default bucket
$cb->set("a", 1);
var_dump($cb->get("a"));
?>

Now, let's say at some point 1.1.1.1 goes down. So, my PHP code is trying to reach a server that is unavailable. What happens then? Did the sdk previously store (remember), the other servers, or am I supposed to try each one in my php code?