Description:
------------
The session handler doesn't support sessions larger than memcached's object/slab size.  Default maximum object size is 1mb.
  
Only error returned is: <error>PHP Warning:  Unknown(): Failed to write session data (memcache). Please verify that the current setting of session.save_path is correct</error>

One possible solution is to define a "max object limit" in the session handler and break apart the session between multiple memcache objects.

Another solution would be to enable compression support in the session handler which would suppress these issues.  

Reproduce code:
---------------
session_start();

$my_string='';

for ($count=0; $count <= 1024*2048; $count++) {
        // printable ascii 32 - 126
        $my_string.= chr(rand(32,126));
}
$_SESSION['big_string']= $my_string;