Memcache may not work, how to configure config.php for memcache?

[postcd]

Hello,

my caching plugin vB Optimize says this when runing test:

Running Test: Fetch Cache
" Your Opcache Operator extension is functioning, however it is unable to store data. Please check your extension configuration."

The operator is set to Memcache.

And this is from phpinfo:

memcache support enabled
Active persistent connections 0
Version 2.2.7
Revision $Revision: 327750 $

Directive Local Value Master Value
memcache.allow_failover 1 1
memcache.chunk_size 8192 8192
memcache.default_port 11211 11211
memcache.default_timeout_ms 1000 1000
memcache.hash_function crc32 crc32
memcache.hash_strategy standard standard
memcache.max_failover_attempts 20 20

This is from vbulletin config.php

/*
$config['Datastore']['class'] = 'vB_Datastore_Memcached';
$i = 0;
// First Server
$i++;
$config['Misc']['memcacheserver'][$i] = '127.0.0.1';
$config['Misc']['memcacheport'][$i] = 11211;
$config['Misc']['memcachepersistent'][$i] = true;
$config['Misc']['memcacheweight'][$i] = 1;
$config['Misc']['memcachetimeout'][$i] = 1;
$config['Misc']['memcacheretry_interval'][$i] = 15;
*/

i wanted to ask what steps to do to fix this? Thank you