Using redis to store sessions

Hi

Using php7 FPM, CodeIgniter 3.1.2, Redis 3.0.3.

After struggling for few hours finding the best setup for using Redis as store engine for sessions I find myself even more confused.
I have tried the following setups, and I will be glad if you have some insights of how this should be working.

Setup 1: 
codeignier config

PHP Code:

$config['sess_driver']          = 'redis';
$config['sess_save_path']       = 'tcp://redis_server_ip:server_port?auth=password&database=0&timeout=604800'; 


php.ini as left with default configuration.
used session_write_close() immediately after updating session data.

Result: 
Codeigniter is using Redis for storing sessions but then I came across this error on heavy ajax pages:
Session: Session: Error while trying to free lock for ci_session:cq399b646bc6lstdhrcrb69k7nvu42r8:lock
I understand the logic and need of lock mechanism but anyway, it seems like CodeIgniter is not handling multiple ajax requests simultaneously.

Setup 2:
codeignier config

PHP Code:

$config['sess_driver']          = 'files'; 


php.ini 

Code:

session.save_handler = redis
session.save_path = "tcp://redis_server_ip:server_port?auth=password&database=0&timeout=604800"

Result:
nothing works!
I get the following error: 
Message: is_dir(): Unable to find the wrapper "tcp" - did you forget to enable it when you configured PHP?
Filename: drivers/Session_files_driver.php
Line Number: 134

Do you guys have any idea of what should be the best way to use redis for storing sessions?